diff --git a/data/json/itemgroups/Labs/lab_security.json b/data/json/itemgroups/Labs/lab_security.json
index 7e996f5a73f5c..aeb6f3c557fdf 100644
--- a/data/json/itemgroups/Labs/lab_security.json
+++ b/data/json/itemgroups/Labs/lab_security.json
@@ -63,34 +63,11 @@
     "//": "This group is for rare spawns of rivetech matched sets.",
     "subtype": "distribution",
     "entries": [
-      { "group": "SUS_rivtech_20x66", "prob": 40 },
       { "group": "SUS_rivtech_8x40", "prob": 80 },
       { "group": "SUS_rivtech_40mm", "prob": 60 },
       { "group": "SUS_rivtech_misc", "prob": 60 }
     ]
   },
-  {
-    "id": "SUS_rivtech_20x66",
-    "type": "item_group",
-    "//": "This group is for rare spawns of rivetech matched sets.",
-    "subtype": "collection",
-    "entries": [
-      { "item": "20x66_10_mag" },
-      {
-        "distribution": [
-          { "item": "20x66_beanbag", "prob": 60, "count": [ 1, 3 ] },
-          { "item": "20x66_exp", "prob": 10, "count": [ 1, 3 ] },
-          { "item": "20x66_flare", "prob": 40, "count": [ 1, 3 ] },
-          { "item": "20x66_frag", "prob": 30, "count": [ 1, 3 ] },
-          { "item": "20x66_shot", "prob": 60, "count": [ 1, 3 ] },
-          { "item": "20x66_slug", "prob": 60, "count": [ 1, 3 ] }
-        ]
-      },
-      {
-        "distribution": [ { "item": "rm120c", "prob": 50 }, { "item": "rm20", "prob": 50 }, { "item": "rm228", "prob": 40 } ]
-      }
-    ]
-  },
   {
     "id": "SUS_rivtech_8x40",
     "type": "item_group",
@@ -142,7 +119,6 @@
     "subtype": "distribution",
     "entries": [
       { "item": "recipe_caseless", "prob": 50 },
-      { "item": "rm121aux", "prob": 50 },
       {
         "collection": [ { "item": "rx12_injector" }, { "item": "ampoule", "prob": 60, "count": [ 1, 3 ] } ],
         "prob": 60
diff --git a/data/json/itemgroups/Locations_MapExtras/locations.json b/data/json/itemgroups/Locations_MapExtras/locations.json
index 79c825170ab48..5fd2753bd7cce 100644
--- a/data/json/itemgroups/Locations_MapExtras/locations.json
+++ b/data/json/itemgroups/Locations_MapExtras/locations.json
@@ -1478,9 +1478,6 @@
       { "item": "remington_870_express", "prob": 1, "charges": [ 0, 7 ] },
       { "item": "benelli_tsa", "variant": "mossberg_500_security", "prob": 1, "charges": [ 0, 6 ] },
       { "item": "shot_beanbag", "prob": 25, "charges": [ 1, 10 ] },
-      { "item": "rm120c", "prob": 2, "charges": [ 0, 5 ] },
-      { "item": "rm20", "prob": 1, "charges": [ 0, 20 ] },
-      { "item": "20x66_beanbag", "prob": 10, "charges": [ 1, 10 ] },
       { "item": "gasbomb", "count": [ 1, 6 ], "prob": 20 },
       { "item": "m79", "prob": 8, "charges": 0 },
       { "item": "40x46mm_m651", "prob": 20, "charges": [ 1, 6 ] },
diff --git a/data/json/itemgroups/Locations_MapExtras/locations_commercial.json b/data/json/itemgroups/Locations_MapExtras/locations_commercial.json
index ebb6d7d8e76fd..e621f45799c23 100644
--- a/data/json/itemgroups/Locations_MapExtras/locations_commercial.json
+++ b/data/json/itemgroups/Locations_MapExtras/locations_commercial.json
@@ -530,7 +530,6 @@
       [ "atomic_coffeepot", 1 ],
       [ "flaregun", 10 ],
       [ "signal_flare", 15 ],
-      [ "rm120c", 2 ],
       [ "knee_pads", 10 ],
       { "item": "oxygen_tank", "prob": 10, "charges": 24 },
       { "item": "smoxygen_tank", "prob": 5, "charges": 12 },
diff --git a/data/json/itemgroups/Weapons_Mods_Ammo/ammo.json b/data/json/itemgroups/Weapons_Mods_Ammo/ammo.json
index 30c33a773d5b3..eab497f2ffb5f 100644
--- a/data/json/itemgroups/Weapons_Mods_Ammo/ammo.json
+++ b/data/json/itemgroups/Weapons_Mods_Ammo/ammo.json
@@ -528,28 +528,14 @@
     "id": "ammo_shotgun_rare",
     "//": "Less common shotgun ammo including that only used by police/paramilitary forces.",
     "subtype": "distribution",
-    "entries": [
-      { "item": "20x66_beanbag", "prob": 10 },
-      { "item": "20x66_flare", "prob": 10 },
-      { "item": "20x66_shot", "prob": 40 },
-      { "item": "20x66_slug", "prob": 20 },
-      { "item": "shot_dragon", "prob": 10 },
-      { "item": "shot_beanbag", "prob": 20 }
-    ]
+    "entries": [ { "item": "shot_dragon", "prob": 10 }, { "item": "shot_beanbag", "prob": 20 } ]
   },
   {
     "type": "item_group",
     "id": "ammo_shotgun_rare_collection",
     "//": "Less common shotgun ammo including that only used by police/paramilitary forces.",
     "subtype": "collection",
-    "entries": [
-      { "item": "20x66_beanbag", "prob": 20 },
-      { "item": "20x66_flare", "prob": 20 },
-      { "item": "20x66_shot", "prob": 80 },
-      { "item": "20x66_slug", "prob": 40 },
-      { "item": "shot_dragon", "prob": 20 },
-      { "item": "shot_beanbag", "prob": 40 }
-    ]
+    "entries": [ { "item": "shot_dragon", "prob": 20 }, { "item": "shot_beanbag", "prob": 40 } ]
   },
   {
     "type": "item_group",
diff --git a/data/json/itemgroups/Weapons_Mods_Ammo/guns.json b/data/json/itemgroups/Weapons_Mods_Ammo/guns.json
index 4a19cf556e87c..42458801c1a34 100644
--- a/data/json/itemgroups/Weapons_Mods_Ammo/guns.json
+++ b/data/json/itemgroups/Weapons_Mods_Ammo/guns.json
@@ -630,7 +630,6 @@
     "//": "Military shotguns currently in service.",
     "//2": "Making the assumption any loaded gun will have additional ammo and mags with it.",
     "items": [
-      { "group": "nested_rm20", "prob": 1 },
       { "group": "nested_remington_870_express", "prob": 50 },
       { "group": "nested_remington_870_breacher", "prob": 20 },
       { "group": "nested_mossberg_590", "prob": 50 },
diff --git a/data/json/itemgroups/Weapons_Mods_Ammo/nested_ammo.json b/data/json/itemgroups/Weapons_Mods_Ammo/nested_ammo.json
index 443aa69768f73..cfe0f7ea9d344 100644
--- a/data/json/itemgroups/Weapons_Mods_Ammo/nested_ammo.json
+++ b/data/json/itemgroups/Weapons_Mods_Ammo/nested_ammo.json
@@ -573,23 +573,6 @@
       { "item": "410shot_slug", "prob": 174, "charges": [ 44, 80 ] }
     ]
   },
-  {
-    "id": "on_hand_20x66mm",
-    "type": "item_group",
-    "//": "a collection of ammo that would be found with a loaded gun.",
-    "subtype": "distribution",
-    "entries": [
-      { "item": "20x66_shot", "prob": 100, "charges": [ 1, 20 ] },
-      { "item": "20x66_shot", "prob": 75, "charges": [ 22, 40 ] },
-      { "item": "20x66_shot", "prob": 30, "charges": [ 44, 80 ] },
-      { "item": "20x66_beanbag", "prob": 30, "charges": [ 1, 20 ] },
-      { "item": "20x66_exp", "prob": 30, "charges": [ 1, 20 ] },
-      { "item": "20x66_frag", "prob": 30, "charges": [ 1, 20 ] },
-      { "item": "20x66_slug", "prob": 100, "charges": [ 1, 20 ] },
-      { "item": "20x66_slug", "prob": 75, "charges": [ 22, 40 ] },
-      { "item": "20x66_slug", "prob": 30, "charges": [ 44, 80 ] }
-    ]
-  },
   {
     "id": "on_hand_50beowulf",
     "type": "item_group",
diff --git a/data/json/itemgroups/Weapons_Mods_Ammo/nested_guns.json b/data/json/itemgroups/Weapons_Mods_Ammo/nested_guns.json
index feb057f3d26b0..b3c01e9c908a4 100644
--- a/data/json/itemgroups/Weapons_Mods_Ammo/nested_guns.json
+++ b/data/json/itemgroups/Weapons_Mods_Ammo/nested_guns.json
@@ -2325,19 +2325,6 @@
       { "group": "on_hand_shot" }
     ]
   },
-  {
-    "id": "nested_rm20",
-    "type": "item_group",
-    "//": "this is a distribution for the gun, reasonable number of backup mags, and some ammo to repack",
-    "subtype": "collection",
-    "ammo": 100,
-    "entries": [
-      { "item": "rm20", "charges": [ 0, 20 ] },
-      { "item": "20x66_20_mag" },
-      { "item": "20x66_20_mag", "prob": 50 },
-      { "group": "on_hand_20x66mm" }
-    ]
-  },
   {
     "id": "nested_mossberg_590",
     "type": "item_group",
diff --git a/data/json/itemgroups/military.json b/data/json/itemgroups/military.json
index 0e7156c27d229..65ccdbe0d691c 100644
--- a/data/json/itemgroups/military.json
+++ b/data/json/itemgroups/military.json
@@ -625,11 +625,6 @@
       { "item": "40x46mm_m651", "prob": 5 },
       { "item": "40x46mm_m576", "prob": 12 },
       { "item": "40x53mm_m1001", "prob": 6 },
-      { "item": "20x66_shot", "prob": 4 },
-      { "item": "20x66_exp", "prob": 1 },
-      { "item": "20x66_flare", "prob": 2 },
-      { "item": "20x66_frag", "prob": 1 },
-      { "item": "20x66_slug", "prob": 4 },
       { "item": "m9", "variant": "m9", "prob": 6 },
       { "item": "usp_45", "prob": 6 },
       { "group": "modular_m4a1", "prob": 7 },
diff --git a/data/json/items/ammo/20x66mm.json b/data/json/items/ammo/20x66mm.json
deleted file mode 100644
index cb11f8d4d83f2..0000000000000
--- a/data/json/items/ammo/20x66mm.json
+++ /dev/null
@@ -1,182 +0,0 @@
-[
-  {
-    "abstract": "20x66_abstract",
-    "type": "AMMO",
-    "name": { "str_sp": "20x66 abstract" },
-    "ascii_picture": "20x66_abstract",
-    "weight": "66 g",
-    "volume": "415 ml",
-    "flags": [ "IRREPLACEABLE_CONSUMABLE" ],
-    "material": [ "plastic", "steel", "powder" ],
-    "//": "0.747, 766gr BalProd rifled Slug+sabot, 313.6gr Vihtavuori 20N29 *C",
-    "damage": {
-      "damage_type": "bullet",
-      "amount": 39,
-      "armor_penetration": 8,
-      "barrels": [
-        { "barrel_length": "28 mm", "amount": 16 },
-        { "barrel_length": "30 mm", "amount": 17 },
-        { "barrel_length": "33 mm", "amount": 18 },
-        { "barrel_length": "38 mm", "amount": 19 },
-        { "barrel_length": "41 mm", "amount": 20 },
-        { "barrel_length": "43 mm", "amount": 21 },
-        { "barrel_length": "46 mm", "amount": 22 },
-        { "barrel_length": "52 mm", "amount": 23 },
-        { "barrel_length": "55 mm", "amount": 24 },
-        { "barrel_length": "58 mm", "amount": 25 },
-        { "barrel_length": "65 mm", "amount": 26 },
-        { "barrel_length": "68 mm", "amount": 27 },
-        { "barrel_length": "74 mm", "amount": 28 },
-        { "barrel_length": "80 mm", "amount": 29 },
-        { "barrel_length": "83 mm", "amount": 30 },
-        { "barrel_length": "89 mm", "amount": 31 },
-        { "barrel_length": "96 mm", "amount": 32 },
-        { "barrel_length": "102 mm", "amount": 33 },
-        { "barrel_length": "108 mm", "amount": 34 },
-        { "barrel_length": "117 mm", "amount": 35 },
-        { "barrel_length": "123 mm", "amount": 36 },
-        { "barrel_length": "133 mm", "amount": 37 },
-        { "barrel_length": "139 mm", "amount": 38 },
-        { "barrel_length": "148 mm", "amount": 39 },
-        { "barrel_length": "157 mm", "amount": 40 },
-        { "barrel_length": "167 mm", "amount": 41 },
-        { "barrel_length": "176 mm", "amount": 42 },
-        { "barrel_length": "188 mm", "amount": 43 },
-        { "barrel_length": "198 mm", "amount": 44 },
-        { "barrel_length": "210 mm", "amount": 45 },
-        { "barrel_length": "223 mm", "amount": 46 },
-        { "barrel_length": "235 mm", "amount": 47 },
-        { "barrel_length": "250 mm", "amount": 48 },
-        { "barrel_length": "266 mm", "amount": 49 },
-        { "barrel_length": "278 mm", "amount": 50 },
-        { "barrel_length": "297 mm", "amount": 51 },
-        { "barrel_length": "312 mm", "amount": 52 },
-        { "barrel_length": "331 mm", "amount": 53 },
-        { "barrel_length": "350 mm", "amount": 54 },
-        { "barrel_length": "371 mm", "amount": 55 },
-        { "barrel_length": "390 mm", "amount": 56 },
-        { "barrel_length": "415 mm", "amount": 57 },
-        { "barrel_length": "436 mm", "amount": 58 },
-        { "barrel_length": "461 mm", "amount": 59 },
-        { "barrel_length": "489 mm", "amount": 60 },
-        { "barrel_length": "517 mm", "amount": 61 },
-        { "barrel_length": "545 mm", "amount": 62 },
-        { "barrel_length": "576 mm", "amount": 63 },
-        { "barrel_length": "610 mm", "amount": 64 },
-        { "barrel_length": "644 mm", "amount": 65 },
-        { "barrel_length": "681 mm", "amount": 66 },
-        { "barrel_length": "718 mm", "amount": 67 },
-        { "barrel_length": "758 mm", "amount": 68 },
-        { "barrel_length": "802 mm", "amount": 69 },
-        { "barrel_length": "848 mm", "amount": 70 },
-        { "barrel_length": "898 mm", "amount": 71 },
-        { "barrel_length": "947 mm", "amount": 72 },
-        { "barrel_length": "1003 mm", "amount": 73 },
-        { "barrel_length": "1062 mm", "amount": 74 },
-        { "barrel_length": "1121 mm", "amount": 75 },
-        { "barrel_length": "1186 mm", "amount": 76 },
-        { "barrel_length": "1239 mm", "amount": 77 }
-      ]
-    },
-    "symbol": "=",
-    "color": "pink",
-    "count": 20,
-    "stack_size": 20,
-    "ammo_type": "20x66mm",
-    "effects": [ "COOKOFF", "NEVER_MISFIRES" ]
-  },
-  {
-    "id": "20x66_beanbag",
-    "copy-from": "20x66_abstract",
-    "type": "AMMO",
-    "name": { "str": "20x66mm beanbag" },
-    "description": "A 20x66mm caseless shotgun round, sublethal beanbag type.  Proprietary ammunition for Rivtech shotguns.",
-    "ascii_picture": "20x66_beanbag",
-    "weight": "21 g",
-    "price": "80 USD",
-    "price_postapoc": "10 USD",
-    "material": [ "plastic", "powder" ],
-    "count": 10,
-    "extend": { "effects": [ "LARGE_BEANBAG", "NOGIB", "CASELESS_ROUNDS" ] },
-    "range": 12,
-    "relative": { "damage": { "damage_type": "bullet", "amount": -33, "armor_penetration": -8 } },
-    "recoil": 1500
-  },
-  {
-    "id": "20x66_exp",
-    "copy-from": "20x66_abstract",
-    "type": "AMMO",
-    "name": { "str_sp": "20x66mm explosive" },
-    "description": "A 20x66mm caseless shotgun round, explosive projectile type.  Proprietary ammunition for Rivtech shotguns.",
-    "price": "100 USD",
-    "price_postapoc": "80 USD",
-    "range": 20,
-    "relative": { "damage": { "damage_type": "bullet", "amount": -23, "armor_penetration": -4 } },
-    "dispersion": 120,
-    "extend": { "effects": [ "EXPLOSIVE_20x66" ], "flags": [ "CASELESS_ROUNDS" ] }
-  },
-  {
-    "id": "20x66_flare",
-    "copy-from": "20x66_abstract",
-    "type": "AMMO",
-    "name": { "str": "20x66mm flare" },
-    "description": "A 20x66mm caseless shotgun round, signal flare type.  Proprietary ammunition for Rivtech shotguns.",
-    "ascii_picture": "20x66_flare",
-    "weight": "21 g",
-    "price": "50 USD",
-    "price_postapoc": "40 USD",
-    "material": [ "plastic", "powder" ],
-    "count": 10,
-    "range": 20,
-    "relative": { "damage": { "damage_type": "bullet", "amount": -23, "armor_penetration": -8 } },
-    "dispersion": 200,
-    "recoil": 100,
-    "drop": "sigflare_lit",
-    "effects": [ "NO_EMBED" ],
-    "extend": { "flags": [ "CASELESS_ROUNDS" ] }
-  },
-  {
-    "id": "20x66_frag",
-    "copy-from": "20x66_slug",
-    "type": "AMMO",
-    "name": { "str_sp": "20x66mm frag" },
-    "description": "A 20x66mm caseless shotgun round, explosive fragmentation type.  Proprietary ammunition for Rivtech shotguns.",
-    "price": "78 USD",
-    "price_postapoc": "50 USD",
-    "count": 5,
-    "extend": { "effects": [ "FRAG_20x66" ], "flags": [ "CASELESS_ROUNDS" ] },
-    "proportional": { "damage": { "damage_type": "bullet", "amount": 0.25, "armor_penetration": 0.25 } }
-  },
-  {
-    "id": "20x66_shot",
-    "copy-from": "20x66_abstract",
-    "type": "AMMO",
-    "name": { "str_sp": "20x66mm buckshot" },
-    "//": "2.5x the Generic Rate of $1/shot",
-    "description": "A 20x66mm caseless shotgun round, loaded with 18 buffered pellets of premium plated 00 buck.  Proprietary ammunition for Rivtech shotguns.",
-    "price": "15 USD",
-    "price_postapoc": "40 USD",
-    "material": [ "lead", "plastic", "powder" ],
-    "range": 12,
-    "projectile_count": 18,
-    "shot_spread": 300,
-    "shot_damage": { "damage_type": "bullet", "amount": 16 },
-    "relative": { "damage": { "damage_type": "bullet", "amount": 11, "armor_penetration": -8 } },
-    "recoil": 3000,
-    "extend": { "effects": [ "SHOT" ], "flags": [ "CASELESS_ROUNDS" ] }
-  },
-  {
-    "id": "20x66_slug",
-    "copy-from": "20x66_abstract",
-    "type": "AMMO",
-    "name": { "str": "20x66mm slug" },
-    "description": "A 20x66mm caseless shotgun round, solid projectile type.  Proprietary ammunition for Rivtech shotguns.",
-    "price": "15 USD",
-    "price_postapoc": "40 USD",
-    "material": [ "lead", "plastic", "powder" ],
-    "range": 24,
-    "dispersion": 100,
-    "recoil": 3000,
-    "extend": { "flags": [ "CASELESS_ROUNDS" ] }
-  }
-]
diff --git a/data/json/items/ammo_types.json b/data/json/items/ammo_types.json
index 659b908289d23..bd7e3c9d98835 100644
--- a/data/json/items/ammo_types.json
+++ b/data/json/items/ammo_types.json
@@ -570,6 +570,7 @@
     "default": "8mm_caseless"
   },
   {
+    "//": "To-do: Remove when 20x66 is fully obsoleted",
     "type": "ammunition_type",
     "id": "20x66mm",
     "name": "20x66mm caseless shotgun",
diff --git a/data/json/items/armor/ammo_pouch.json b/data/json/items/armor/ammo_pouch.json
index 194f17161ade8..431acc68f8e36 100644
--- a/data/json/items/armor/ammo_pouch.json
+++ b/data/json/items/armor/ammo_pouch.json
@@ -53,7 +53,6 @@
           "308": 60,
           "12mm": 60,
           "8x40mm": 60,
-          "20x66mm": 60,
           "stimpack_ammo": 60,
           "ampoule": 60,
           "300": 60,
@@ -652,7 +651,7 @@
         "volume_encumber_modifier": 0.25
       },
       {
-        "ammo_restriction": { "410shot": 6, "shot": 6, "20x66mm": 6, "signal_flare": 6 },
+        "ammo_restriction": { "410shot": 6, "shot": 6, "signal_flare": 6 },
         "moves": 25,
         "volume_encumber_modifier": 0.2
       }
@@ -1253,7 +1252,7 @@
     "symbol": "[",
     "looks_like": "holster",
     "color": "dark_gray",
-    "pocket_data": [ { "ammo_restriction": { "410shot": 12, "shot": 12, "20x66mm": 12, "signal_flare": 12, "308": 20 }, "moves": 30 } ],
+    "pocket_data": [ { "ammo_restriction": { "410shot": 12, "shot": 12, "signal_flare": 12, "308": 20 }, "moves": 30 } ],
     "material_thickness": 0.5,
     "flags": [ "BELTED", "OVERSIZE", "WATER_FRIENDLY", "PALS_MEDIUM" ],
     "armor": [ { "encumbrance": 2, "coverage": 100, "covers": [ "torso" ], "specifically_covers": [ "torso_waist" ] } ]
diff --git a/data/json/items/armor/bandolier.json b/data/json/items/armor/bandolier.json
index 7ba1c849ca503..9bdfa43394623 100644
--- a/data/json/items/armor/bandolier.json
+++ b/data/json/items/armor/bandolier.json
@@ -103,11 +103,7 @@
     "color": "dark_gray",
     "material_thickness": 1,
     "pocket_data": [
-      {
-        "ammo_restriction": { "410shot": 25, "shot": 25, "20x66mm": 25, "signal_flare": 25 },
-        "moves": 25,
-        "volume_encumber_modifier": 0.3
-      }
+      { "ammo_restriction": { "410shot": 25, "shot": 25, "signal_flare": 25 }, "moves": 25, "volume_encumber_modifier": 0.3 }
     ],
     "flags": [ "WATER_FRIENDLY", "BELTED", "OVERSIZE" ],
     "armor": [ { "encumbrance": 2, "coverage": 100, "covers": [ "torso" ], "specifically_covers": [ "torso_waist" ] } ]
@@ -138,11 +134,7 @@
     "color": "dark_gray",
     "material_thickness": 1,
     "pocket_data": [
-      {
-        "ammo_restriction": { "410shot": 50, "shot": 50, "20x66mm": 50, "signal_flare": 50 },
-        "moves": 35,
-        "volume_encumber_modifier": 0.3
-      }
+      { "ammo_restriction": { "410shot": 50, "shot": 50, "signal_flare": 50 }, "moves": 35, "volume_encumber_modifier": 0.3 }
     ],
     "flags": [ "WATER_FRIENDLY", "OVERSIZE", "BELTED" ],
     "armor": [ { "encumbrance": 3, "coverage": 20, "covers": [ "torso" ], "specifically_covers": [ "torso_upper" ] } ]
diff --git a/data/json/items/gun/20x66mm.json b/data/json/items/gun/20x66mm.json
deleted file mode 100644
index ef56e3036c787..0000000000000
--- a/data/json/items/gun/20x66mm.json
+++ /dev/null
@@ -1,138 +0,0 @@
-[
-  {
-    "id": "rm120c",
-    "looks_like": "remington_870",
-    "type": "GUN",
-    "reload_noise_volume": 10,
-    "reload_noise": "chuk chuk.",
-    "name": { "str": "caseless hunting shotgun" },
-    "description": "Designed by Rivtech and utilizing a powerful and unusual caliber, this caseless pump-action shotgun was designed for hunting big game, with durability and ease of use as priorities.",
-    "variant_type": "gun",
-    "variants": [
-      {
-        "id": "rm120c",
-        "name": { "str": "RM120c shotgun" },
-        "description": "Utilizing a powerful and unusual caliber, the Rivtech RM120c caseless pump-action shotgun was designed for hunting big game, with durability and ease of use as priorities."
-      }
-    ],
-    "weight": "2480 g",
-    "volume": "2250 ml",
-    "longest_side": "920 mm",
-    "barrel_length": "470 mm",
-    "price": "3 kUSD 100 USD",
-    "price_postapoc": "22 USD 50 cent",
-    "to_hit": -1,
-    "material": [ "superalloy", "ceramic" ],
-    "symbol": "(",
-    "color": "dark_gray",
-    "ammo": [ "20x66mm" ],
-    "skill": "shotgun",
-    "range": 6,
-    "dispersion": 285,
-    "durability": 9,
-    "clip_size": 5,
-    "barrel_volume": "750 ml",
-    "valid_mod_locations": [
-      [ "grip", 1 ],
-      [ "mechanism", 2 ],
-      [ "muzzle", 1 ],
-      [ "rail", 1 ],
-      [ "sights", 1 ],
-      [ "sling", 1 ],
-      [ "stock", 1 ],
-      [ "stock accessory", 2 ],
-      [ "underbarrel", 1 ]
-    ],
-    "flags": [ "RELOAD_ONE", "WATERPROOF_GUN", "NEVER_JAMS", "PUMP_ACTION" ],
-    "pocket_data": [ { "pocket_type": "MAGAZINE", "rigid": true, "ammo_restriction": { "20x66mm": 5 } } ],
-    "melee_damage": { "bash": 8 }
-  },
-  {
-    "id": "rm20",
-    "looks_like": "remington_870",
-    "type": "GUN",
-    "reload_noise_volume": 10,
-    "name": { "str": "RM20 caseless autoshotgun" },
-    "description": "Designed by Rivtech and utilizing a powerful and unusual caliber, this caseless automatic combat shotgun was designed with durability and overwhelming power in mind.",
-    "variant_type": "gun",
-    "variants": [
-      {
-        "id": "rm20",
-        "name": { "str": "RM20 autoshotgun" },
-        "description": "Utilizing a powerful and unusual caliber, the Rivtech RM20 caseless automatic combat shotgun was designed with durability and overwhelming power in mind."
-      }
-    ],
-    "weight": "2920 g",
-    "volume": "2450 ml",
-    "longest_side": "775 mm",
-    "barrel_length": "470 mm",
-    "price": "13 kUSD 200 USD",
-    "price_postapoc": "100 USD",
-    "to_hit": -1,
-    "material": [ "superalloy", "ceramic" ],
-    "symbol": "(",
-    "color": "dark_gray",
-    "ammo": [ "20x66mm" ],
-    "skill": "shotgun",
-    "dispersion": 335,
-    "durability": 9,
-    "modes": [ [ "DEFAULT", "semi-auto", 1 ], [ "AUTO", "auto", 2 ] ],
-    "valid_mod_locations": [
-      [ "grip", 1 ],
-      [ "mechanism", 2 ],
-      [ "muzzle", 1 ],
-      [ "rail", 1 ],
-      [ "sights", 1 ],
-      [ "sling", 1 ],
-      [ "stock", 1 ],
-      [ "stock accessory", 2 ],
-      [ "underbarrel", 1 ]
-    ],
-    "flags": [ "WATERPROOF_GUN", "NEVER_JAMS" ],
-    "pocket_data": [
-      { "magazine_well": "500 ml", "pocket_type": "MAGAZINE_WELL", "item_restriction": [ "20x66_20_mag", "20x66_40_mag" ] }
-    ],
-    "melee_damage": { "bash": 11 }
-  },
-  {
-    "id": "rm228",
-    "looks_like": "remington_870",
-    "type": "GUN",
-    "reload_noise_volume": 10,
-    "name": { "str": "compact caseless shotgun" },
-    "description": "Designed by Rivtech and designated the RM228 PDW, chambering the powerful 20x66mm caseless shotgun cartridge, this gun was designed for the civilian personal defense market with durability and ease of use as priorities.  While lauded for its small size and light weight, its hefty price tag kept it out of the reach of casual collectors.",
-    "variant_type": "gun",
-    "variants": [
-      {
-        "id": "rm228",
-        "name": { "str": "RM228 PDW" },
-        "description": "Chambering the powerful 20x66mm caseless shotgun cartridge, the Rivtech RM228 PDW was designed for the civilian personal defense market with durability and ease of use as priorities.  While lauded for its small size and light weight, its hefty price tag kept it out of the reach of casual collectors."
-      }
-    ],
-    "weight": "780 g",
-    "volume": "750 ml",
-    "longest_side": "165 mm",
-    "price": "3 kUSD 300 USD",
-    "price_postapoc": "100 USD",
-    "material": [ "superalloy", "ceramic" ],
-    "symbol": "(",
-    "color": "dark_gray",
-    "ammo": [ "20x66mm" ],
-    "skill": "pistol",
-    "dispersion": 400,
-    "durability": 9,
-    "default_mods": [ "pistol_stock" ],
-    "valid_mod_locations": [
-      [ "grip", 1 ],
-      [ "mechanism", 2 ],
-      [ "rail", 1 ],
-      [ "sights", 1 ],
-      [ "stock", 1 ],
-      [ "stock accessory", 2 ],
-      [ "underbarrel mount", 1 ]
-    ],
-    "flags": [ "WATERPROOF_GUN", "NEVER_JAMS" ],
-    "pocket_data": [ { "magazine_well": "250 ml", "pocket_type": "MAGAZINE_WELL", "item_restriction": [ "20x66_10_mag" ] } ],
-    "melee_damage": { "bash": 6 }
-  }
-]
diff --git a/data/json/items/gunmod/underbarrel.json b/data/json/items/gunmod/underbarrel.json
index 94ad6fb974abc..649e3102fe431 100644
--- a/data/json/items/gunmod/underbarrel.json
+++ b/data/json/items/gunmod/underbarrel.json
@@ -454,45 +454,6 @@
     "flags": [  ],
     "melee_damage": { "stab": 6 }
   },
-  {
-    "id": "rm121aux",
-    "copy-from": "underbarrel_base",
-    "type": "GUNMOD",
-    "name": { "str": "caseless aux shotgun" },
-    "description": "Designated the Rivtech RM121 auxiliary weapon system, this is a magazine-fed semi-automatic caseless shotgun, which can be mounted under the barrel of many rifles.  Accepts RMSA10 box magazines.",
-    "variant_type": "gun",
-    "variants": [
-      {
-        "id": "rm121aux",
-        "name": { "str": "RM121 aux shotgun" },
-        "description": "The Rivtech RM121 auxiliary weapon system is a magazine-fed semi-automatic caseless shotgun, which can be mounted under the barrel of many rifles.  Accepts RMSA10 box magazines."
-      }
-    ],
-    "weight": "1140 g",
-    "volume": "750 ml",
-    "longest_side": "380 mm",
-    "price": "1 kUSD 200 USD",
-    "price_postapoc": "50 USD",
-    "install_time": "5 m",
-    "material": [ "superalloy", "ceramic" ],
-    "symbol": ":",
-    "color": "dark_gray",
-    "location": "underbarrel",
-    "blacklist_mod": [ "knife_combat_army", "knife_combat", "enfield_bayonet", "knife_combat_marine", "makeshift_bayonet", "sword_bayonet" ],
-    "mod_targets": [ "rifle", "crossbow" ],
-    "gun_data": { "barrel_length": "419 mm", "ammo": "20x66mm", "skill": "shotgun", "dispersion": 320, "durability": 9, "reload": 125 },
-    "min_skills": [ [ "weapon", 2 ], [ "shotgun", 2 ] ],
-    "flags": [ "WATERPROOF_GUN", "NEVER_JAMS" ],
-    "pocket_data": [ { "pocket_type": "MAGAZINE_WELL", "item_restriction": [ "20x66_10_mag" ] } ]
-  },
-  {
-    "id": "rm121aux_mod",
-    "copy-from": "rm121aux",
-    "type": "GUNMOD",
-    "name": { "str": "modified RM121 aux shotgun" },
-    "description": "The Rivtech RM121 auxiliary weapon system is a magazine-fed semi-automatic caseless shotgun, which can be mounted under the barrel of many rifles.  Accepts RMSA10 box magazines.  This one was modified and customized to mount on pretty much any weapon other than pistols, if you so want.",
-    "mod_targets": [ "smg", "rifle", "shotgun", "launcher", "crossbow" ]
-  },
   {
     "id": "u_shotgun",
     "copy-from": "underbarrel_base",
diff --git a/data/json/items/magazine/20x60mm.json b/data/json/items/magazine/20x60mm.json
deleted file mode 100644
index f874e4f3d44f0..0000000000000
--- a/data/json/items/magazine/20x60mm.json
+++ /dev/null
@@ -1,56 +0,0 @@
-[
-  {
-    "id": "20x66_10_mag",
-    "looks_like": "shotbelt_20",
-    "type": "MAGAZINE",
-    "name": { "str": "compact caseless 10-round magazine" },
-    "description": "A 10-round box magazine for use with the RM228 PDW and RM121 auxiliary shotgun.  Designated as RMSA10.",
-    "weight": "210 g",
-    "volume": "250 ml",
-    "price": "400 USD",
-    "price_postapoc": "2 USD 50 cent",
-    "material": [ "superalloy", "plastic" ],
-    "symbol": "#",
-    "color": "dark_gray",
-    "ammo_type": [ "20x66mm" ],
-    "reload_time": 60,
-    "flags": [ "MAG_COMPACT" ],
-    "pocket_data": [ { "pocket_type": "MAGAZINE", "rigid": true, "ammo_restriction": { "20x66mm": 10 } } ]
-  },
-  {
-    "id": "20x66_20_mag",
-    "looks_like": "shotbelt_20",
-    "type": "MAGAZINE",
-    "name": { "str": "RM20 20-round magazine" },
-    "description": "A 20-round box magazine for use with the RM20 caseless shotgun.  Designated as RMSB20.",
-    "weight": "280 g",
-    "volume": "500 ml",
-    "price": "400 USD",
-    "price_postapoc": "5 USD",
-    "material": [ "superalloy", "plastic" ],
-    "symbol": "#",
-    "color": "dark_gray",
-    "ammo_type": [ "20x66mm" ],
-    "reload_time": 60,
-    "flags": [ "MAG_COMPACT" ],
-    "pocket_data": [ { "pocket_type": "MAGAZINE", "rigid": true, "ammo_restriction": { "20x66mm": 20 } } ]
-  },
-  {
-    "id": "20x66_40_mag",
-    "looks_like": "shotbelt_20",
-    "type": "MAGAZINE",
-    "name": { "str": "RM20 40-round magazine" },
-    "description": "A 40-round box magazine for use with the RM20 caseless shotgun.  Designated as RMSB40.",
-    "weight": "280 g",
-    "volume": "750 ml",
-    "price": "600 USD",
-    "price_postapoc": "10 USD",
-    "material": [ "superalloy", "plastic" ],
-    "symbol": "#",
-    "color": "dark_gray",
-    "ammo_type": [ "20x66mm" ],
-    "reload_time": 70,
-    "flags": [ "MAG_BULKY" ],
-    "pocket_data": [ { "pocket_type": "MAGAZINE", "rigid": true, "ammo_restriction": { "20x66mm": 40 } } ]
-  }
-]
diff --git a/data/json/npcs/robofac/NPC_Ulysses_Rourke.json b/data/json/npcs/robofac/NPC_Ulysses_Rourke.json
index bdf0221c00af1..f7759b4b29e31 100644
--- a/data/json/npcs/robofac/NPC_Ulysses_Rourke.json
+++ b/data/json/npcs/robofac/NPC_Ulysses_Rourke.json
@@ -55,17 +55,12 @@
   {
     "type": "item_group",
     "id": "NC_robofac_security_head_weapon",
-    "items": [ { "item": "rm20", "charges": 20, "ammo-item": "20x66_slug", "contents-group": "robofac_sec_weapon_mods" } ]
+    "items": [ { "item": "fn_p90", "charges": 50 } ]
   },
   {
     "type": "item_group",
     "id": "NC_robofac_security_head_misc",
     "subtype": "collection",
-    "entries": [
-      { "item": "flashbang", "count": 2 },
-      { "item": "20x66_40_mag", "count": 2, "charges": 40, "ammo-item": "20x66_shot" },
-      { "item": "20x66_beanbag", "count": 1 },
-      { "item": "20x66_frag", "count": 2 }
-    ]
+    "entries": [ { "item": "flashbang", "count": 2 }, { "item": "fnp90mag", "count": 3, "charges": 50 } ]
   }
 ]
diff --git a/data/json/obsoletion_and_migration_0.I/gun.json b/data/json/obsoletion_and_migration_0.I/gun.json
index dfeb6fb9dd633..73ba36741a4d3 100644
--- a/data/json/obsoletion_and_migration_0.I/gun.json
+++ b/data/json/obsoletion_and_migration_0.I/gun.json
@@ -613,5 +613,414 @@
     "weapon_category": [ "AUTOMATIC_RIFLES" ],
     "pocket_data": [ { "pocket_type": "MAGAZINE_WELL", "item_restriction": [ "8x40_100_mag", "8x40_50_mag", "8x40_250_mag" ] } ],
     "melee_damage": { "bash": 12 }
+  },
+  {
+    "id": "rm120c",
+    "looks_like": "remington_870",
+    "type": "GUN",
+    "reload_noise_volume": 10,
+    "reload_noise": "chuk chuk.",
+    "name": { "str": "caseless hunting shotgun" },
+    "description": "Designed by Rivtech and utilizing a powerful and unusual caliber, this caseless pump-action shotgun was designed for hunting big game, with durability and ease of use as priorities.",
+    "variant_type": "gun",
+    "variants": [
+      {
+        "id": "rm120c",
+        "name": { "str": "RM120c shotgun" },
+        "description": "Utilizing a powerful and unusual caliber, the Rivtech RM120c caseless pump-action shotgun was designed for hunting big game, with durability and ease of use as priorities."
+      }
+    ],
+    "weight": "2480 g",
+    "volume": "2250 ml",
+    "longest_side": "920 mm",
+    "barrel_length": "470 mm",
+    "price": "3 kUSD 100 USD",
+    "price_postapoc": "22 USD 50 cent",
+    "to_hit": -1,
+    "material": [ "superalloy", "ceramic" ],
+    "symbol": "(",
+    "color": "dark_gray",
+    "ammo": [ "20x66mm" ],
+    "skill": "shotgun",
+    "range": 6,
+    "dispersion": 285,
+    "durability": 9,
+    "clip_size": 5,
+    "barrel_volume": "750 ml",
+    "valid_mod_locations": [
+      [ "grip", 1 ],
+      [ "mechanism", 2 ],
+      [ "muzzle", 1 ],
+      [ "rail", 1 ],
+      [ "sights", 1 ],
+      [ "sling", 1 ],
+      [ "stock", 1 ],
+      [ "stock accessory", 2 ],
+      [ "underbarrel", 1 ]
+    ],
+    "flags": [ "RELOAD_ONE", "WATERPROOF_GUN", "NEVER_JAMS", "PUMP_ACTION" ],
+    "pocket_data": [ { "pocket_type": "MAGAZINE", "rigid": true, "ammo_restriction": { "20x66mm": 5 } } ],
+    "melee_damage": { "bash": 8 }
+  },
+  {
+    "id": "rm20",
+    "looks_like": "remington_870",
+    "type": "GUN",
+    "reload_noise_volume": 10,
+    "name": { "str": "RM20 caseless autoshotgun" },
+    "description": "Designed by Rivtech and utilizing a powerful and unusual caliber, this caseless automatic combat shotgun was designed with durability and overwhelming power in mind.",
+    "variant_type": "gun",
+    "variants": [
+      {
+        "id": "rm20",
+        "name": { "str": "RM20 autoshotgun" },
+        "description": "Utilizing a powerful and unusual caliber, the Rivtech RM20 caseless automatic combat shotgun was designed with durability and overwhelming power in mind."
+      }
+    ],
+    "weight": "2920 g",
+    "volume": "2450 ml",
+    "longest_side": "775 mm",
+    "barrel_length": "470 mm",
+    "price": "13 kUSD 200 USD",
+    "price_postapoc": "100 USD",
+    "to_hit": -1,
+    "material": [ "superalloy", "ceramic" ],
+    "symbol": "(",
+    "color": "dark_gray",
+    "ammo": [ "20x66mm" ],
+    "skill": "shotgun",
+    "dispersion": 335,
+    "durability": 9,
+    "modes": [ [ "DEFAULT", "semi-auto", 1 ], [ "AUTO", "auto", 2 ] ],
+    "valid_mod_locations": [
+      [ "grip", 1 ],
+      [ "mechanism", 2 ],
+      [ "muzzle", 1 ],
+      [ "rail", 1 ],
+      [ "sights", 1 ],
+      [ "sling", 1 ],
+      [ "stock", 1 ],
+      [ "stock accessory", 2 ],
+      [ "underbarrel", 1 ]
+    ],
+    "flags": [ "WATERPROOF_GUN", "NEVER_JAMS" ],
+    "pocket_data": [
+      { "magazine_well": "500 ml", "pocket_type": "MAGAZINE_WELL", "item_restriction": [ "20x66_20_mag", "20x66_40_mag" ] }
+    ],
+    "melee_damage": { "bash": 11 }
+  },
+  {
+    "id": "rm228",
+    "looks_like": "remington_870",
+    "type": "GUN",
+    "reload_noise_volume": 10,
+    "name": { "str": "compact caseless shotgun" },
+    "description": "Designed by Rivtech and designated the RM228 PDW, chambering the powerful 20x66mm caseless shotgun cartridge, this gun was designed for the civilian personal defense market with durability and ease of use as priorities.  While lauded for its small size and light weight, its hefty price tag kept it out of the reach of casual collectors.",
+    "variant_type": "gun",
+    "variants": [
+      {
+        "id": "rm228",
+        "name": { "str": "RM228 PDW" },
+        "description": "Chambering the powerful 20x66mm caseless shotgun cartridge, the Rivtech RM228 PDW was designed for the civilian personal defense market with durability and ease of use as priorities.  While lauded for its small size and light weight, its hefty price tag kept it out of the reach of casual collectors."
+      }
+    ],
+    "weight": "780 g",
+    "volume": "750 ml",
+    "longest_side": "165 mm",
+    "price": "3 kUSD 300 USD",
+    "price_postapoc": "100 USD",
+    "material": [ "superalloy", "ceramic" ],
+    "symbol": "(",
+    "color": "dark_gray",
+    "ammo": [ "20x66mm" ],
+    "skill": "pistol",
+    "dispersion": 400,
+    "durability": 9,
+    "default_mods": [ "pistol_stock" ],
+    "valid_mod_locations": [
+      [ "grip", 1 ],
+      [ "mechanism", 2 ],
+      [ "rail", 1 ],
+      [ "sights", 1 ],
+      [ "stock", 1 ],
+      [ "stock accessory", 2 ],
+      [ "underbarrel mount", 1 ]
+    ],
+    "flags": [ "WATERPROOF_GUN", "NEVER_JAMS" ],
+    "pocket_data": [ { "magazine_well": "250 ml", "pocket_type": "MAGAZINE_WELL", "item_restriction": [ "20x66_10_mag" ] } ],
+    "melee_damage": { "bash": 6 }
+  },
+  {
+    "id": "20x66_10_mag",
+    "looks_like": "shotbelt_20",
+    "type": "MAGAZINE",
+    "name": { "str": "compact caseless 10-round magazine" },
+    "description": "A 10-round box magazine for use with the RM228 PDW and RM121 auxiliary shotgun.  Designated as RMSA10.",
+    "weight": "210 g",
+    "volume": "250 ml",
+    "price": "400 USD",
+    "price_postapoc": "2 USD 50 cent",
+    "material": [ "superalloy", "plastic" ],
+    "symbol": "#",
+    "color": "dark_gray",
+    "ammo_type": [ "20x66mm" ],
+    "reload_time": 60,
+    "flags": [ "MAG_COMPACT" ],
+    "pocket_data": [ { "pocket_type": "MAGAZINE", "rigid": true, "ammo_restriction": { "20x66mm": 10 } } ]
+  },
+  {
+    "id": "20x66_20_mag",
+    "looks_like": "shotbelt_20",
+    "type": "MAGAZINE",
+    "name": { "str": "RM20 20-round magazine" },
+    "description": "A 20-round box magazine for use with the RM20 caseless shotgun.  Designated as RMSB20.",
+    "weight": "280 g",
+    "volume": "500 ml",
+    "price": "400 USD",
+    "price_postapoc": "5 USD",
+    "material": [ "superalloy", "plastic" ],
+    "symbol": "#",
+    "color": "dark_gray",
+    "ammo_type": [ "20x66mm" ],
+    "reload_time": 60,
+    "flags": [ "MAG_COMPACT" ],
+    "pocket_data": [ { "pocket_type": "MAGAZINE", "rigid": true, "ammo_restriction": { "20x66mm": 20 } } ]
+  },
+  {
+    "id": "20x66_40_mag",
+    "looks_like": "shotbelt_20",
+    "type": "MAGAZINE",
+    "name": { "str": "RM20 40-round magazine" },
+    "description": "A 40-round box magazine for use with the RM20 caseless shotgun.  Designated as RMSB40.",
+    "weight": "280 g",
+    "volume": "750 ml",
+    "price": "600 USD",
+    "price_postapoc": "10 USD",
+    "material": [ "superalloy", "plastic" ],
+    "symbol": "#",
+    "color": "dark_gray",
+    "ammo_type": [ "20x66mm" ],
+    "reload_time": 70,
+    "flags": [ "MAG_BULKY" ],
+    "pocket_data": [ { "pocket_type": "MAGAZINE", "rigid": true, "ammo_restriction": { "20x66mm": 40 } } ]
+  },
+  {
+    "abstract": "20x66_abstract",
+    "type": "AMMO",
+    "name": { "str_sp": "20x66 abstract" },
+    "ascii_picture": "20x66_abstract",
+    "weight": "66 g",
+    "volume": "415 ml",
+    "flags": [ "IRREPLACEABLE_CONSUMABLE" ],
+    "material": [ "plastic", "steel", "powder" ],
+    "//": "0.747, 766gr BalProd rifled Slug+sabot, 313.6gr Vihtavuori 20N29 *C",
+    "damage": {
+      "damage_type": "bullet",
+      "amount": 39,
+      "armor_penetration": 8,
+      "barrels": [
+        { "barrel_length": "28 mm", "amount": 16 },
+        { "barrel_length": "30 mm", "amount": 17 },
+        { "barrel_length": "33 mm", "amount": 18 },
+        { "barrel_length": "38 mm", "amount": 19 },
+        { "barrel_length": "41 mm", "amount": 20 },
+        { "barrel_length": "43 mm", "amount": 21 },
+        { "barrel_length": "46 mm", "amount": 22 },
+        { "barrel_length": "52 mm", "amount": 23 },
+        { "barrel_length": "55 mm", "amount": 24 },
+        { "barrel_length": "58 mm", "amount": 25 },
+        { "barrel_length": "65 mm", "amount": 26 },
+        { "barrel_length": "68 mm", "amount": 27 },
+        { "barrel_length": "74 mm", "amount": 28 },
+        { "barrel_length": "80 mm", "amount": 29 },
+        { "barrel_length": "83 mm", "amount": 30 },
+        { "barrel_length": "89 mm", "amount": 31 },
+        { "barrel_length": "96 mm", "amount": 32 },
+        { "barrel_length": "102 mm", "amount": 33 },
+        { "barrel_length": "108 mm", "amount": 34 },
+        { "barrel_length": "117 mm", "amount": 35 },
+        { "barrel_length": "123 mm", "amount": 36 },
+        { "barrel_length": "133 mm", "amount": 37 },
+        { "barrel_length": "139 mm", "amount": 38 },
+        { "barrel_length": "148 mm", "amount": 39 },
+        { "barrel_length": "157 mm", "amount": 40 },
+        { "barrel_length": "167 mm", "amount": 41 },
+        { "barrel_length": "176 mm", "amount": 42 },
+        { "barrel_length": "188 mm", "amount": 43 },
+        { "barrel_length": "198 mm", "amount": 44 },
+        { "barrel_length": "210 mm", "amount": 45 },
+        { "barrel_length": "223 mm", "amount": 46 },
+        { "barrel_length": "235 mm", "amount": 47 },
+        { "barrel_length": "250 mm", "amount": 48 },
+        { "barrel_length": "266 mm", "amount": 49 },
+        { "barrel_length": "278 mm", "amount": 50 },
+        { "barrel_length": "297 mm", "amount": 51 },
+        { "barrel_length": "312 mm", "amount": 52 },
+        { "barrel_length": "331 mm", "amount": 53 },
+        { "barrel_length": "350 mm", "amount": 54 },
+        { "barrel_length": "371 mm", "amount": 55 },
+        { "barrel_length": "390 mm", "amount": 56 },
+        { "barrel_length": "415 mm", "amount": 57 },
+        { "barrel_length": "436 mm", "amount": 58 },
+        { "barrel_length": "461 mm", "amount": 59 },
+        { "barrel_length": "489 mm", "amount": 60 },
+        { "barrel_length": "517 mm", "amount": 61 },
+        { "barrel_length": "545 mm", "amount": 62 },
+        { "barrel_length": "576 mm", "amount": 63 },
+        { "barrel_length": "610 mm", "amount": 64 },
+        { "barrel_length": "644 mm", "amount": 65 },
+        { "barrel_length": "681 mm", "amount": 66 },
+        { "barrel_length": "718 mm", "amount": 67 },
+        { "barrel_length": "758 mm", "amount": 68 },
+        { "barrel_length": "802 mm", "amount": 69 },
+        { "barrel_length": "848 mm", "amount": 70 },
+        { "barrel_length": "898 mm", "amount": 71 },
+        { "barrel_length": "947 mm", "amount": 72 },
+        { "barrel_length": "1003 mm", "amount": 73 },
+        { "barrel_length": "1062 mm", "amount": 74 },
+        { "barrel_length": "1121 mm", "amount": 75 },
+        { "barrel_length": "1186 mm", "amount": 76 },
+        { "barrel_length": "1239 mm", "amount": 77 }
+      ]
+    },
+    "symbol": "=",
+    "color": "pink",
+    "count": 20,
+    "stack_size": 20,
+    "ammo_type": "20x66mm",
+    "effects": [ "COOKOFF", "NEVER_MISFIRES" ]
+  },
+  {
+    "id": "20x66_beanbag",
+    "copy-from": "20x66_abstract",
+    "type": "AMMO",
+    "name": { "str": "20x66mm beanbag" },
+    "description": "A 20x66mm caseless shotgun round, sublethal beanbag type.  Proprietary ammunition for Rivtech shotguns.",
+    "ascii_picture": "20x66_beanbag",
+    "weight": "21 g",
+    "price": "80 USD",
+    "price_postapoc": "10 USD",
+    "material": [ "plastic", "powder" ],
+    "count": 10,
+    "extend": { "effects": [ "LARGE_BEANBAG", "NOGIB", "CASELESS_ROUNDS" ] },
+    "range": 12,
+    "relative": { "damage": { "damage_type": "bullet", "amount": -33, "armor_penetration": -8 } },
+    "recoil": 1500
+  },
+  {
+    "id": "20x66_exp",
+    "copy-from": "20x66_abstract",
+    "type": "AMMO",
+    "name": { "str_sp": "20x66mm explosive" },
+    "description": "A 20x66mm caseless shotgun round, explosive projectile type.  Proprietary ammunition for Rivtech shotguns.",
+    "price": "100 USD",
+    "price_postapoc": "80 USD",
+    "range": 20,
+    "relative": { "damage": { "damage_type": "bullet", "amount": -23, "armor_penetration": -4 } },
+    "dispersion": 120,
+    "extend": { "effects": [ "EXPLOSIVE_20x66" ], "flags": [ "CASELESS_ROUNDS" ] }
+  },
+  {
+    "id": "20x66_flare",
+    "copy-from": "20x66_abstract",
+    "type": "AMMO",
+    "name": { "str": "20x66mm flare" },
+    "description": "A 20x66mm caseless shotgun round, signal flare type.  Proprietary ammunition for Rivtech shotguns.",
+    "ascii_picture": "20x66_flare",
+    "weight": "21 g",
+    "price": "50 USD",
+    "price_postapoc": "40 USD",
+    "material": [ "plastic", "powder" ],
+    "count": 10,
+    "range": 20,
+    "relative": { "damage": { "damage_type": "bullet", "amount": -23, "armor_penetration": -8 } },
+    "dispersion": 200,
+    "recoil": 100,
+    "drop": "sigflare_lit",
+    "effects": [ "NO_EMBED" ],
+    "extend": { "flags": [ "CASELESS_ROUNDS" ] }
+  },
+  {
+    "id": "20x66_frag",
+    "copy-from": "20x66_slug",
+    "type": "AMMO",
+    "name": { "str_sp": "20x66mm frag" },
+    "description": "A 20x66mm caseless shotgun round, explosive fragmentation type.  Proprietary ammunition for Rivtech shotguns.",
+    "price": "78 USD",
+    "price_postapoc": "50 USD",
+    "count": 5,
+    "extend": { "effects": [ "FRAG_20x66" ], "flags": [ "CASELESS_ROUNDS" ] },
+    "proportional": { "damage": { "damage_type": "bullet", "amount": 0.25, "armor_penetration": 0.25 } }
+  },
+  {
+    "id": "20x66_shot",
+    "copy-from": "20x66_abstract",
+    "type": "AMMO",
+    "name": { "str_sp": "20x66mm buckshot" },
+    "//": "2.5x the Generic Rate of $1/shot",
+    "description": "A 20x66mm caseless shotgun round, loaded with 18 buffered pellets of premium plated 00 buck.  Proprietary ammunition for Rivtech shotguns.",
+    "price": "15 USD",
+    "price_postapoc": "40 USD",
+    "material": [ "lead", "plastic", "powder" ],
+    "range": 12,
+    "projectile_count": 18,
+    "shot_spread": 300,
+    "shot_damage": { "damage_type": "bullet", "amount": 16 },
+    "relative": { "damage": { "damage_type": "bullet", "amount": 11, "armor_penetration": -8 } },
+    "recoil": 3000,
+    "extend": { "effects": [ "SHOT" ], "flags": [ "CASELESS_ROUNDS" ] }
+  },
+  {
+    "id": "20x66_slug",
+    "copy-from": "20x66_abstract",
+    "type": "AMMO",
+    "name": { "str": "20x66mm slug" },
+    "description": "A 20x66mm caseless shotgun round, solid projectile type.  Proprietary ammunition for Rivtech shotguns.",
+    "price": "15 USD",
+    "price_postapoc": "40 USD",
+    "material": [ "lead", "plastic", "powder" ],
+    "range": 24,
+    "dispersion": 100,
+    "recoil": 3000,
+    "extend": { "flags": [ "CASELESS_ROUNDS" ] }
+  },
+  {
+    "id": "rm121aux",
+    "copy-from": "underbarrel_base",
+    "type": "GUNMOD",
+    "name": { "str": "caseless aux shotgun" },
+    "description": "Designated the Rivtech RM121 auxiliary weapon system, this is a magazine-fed semi-automatic caseless shotgun, which can be mounted under the barrel of many rifles.  Accepts RMSA10 box magazines.",
+    "variant_type": "gun",
+    "variants": [
+      {
+        "id": "rm121aux",
+        "name": { "str": "RM121 aux shotgun" },
+        "description": "The Rivtech RM121 auxiliary weapon system is a magazine-fed semi-automatic caseless shotgun, which can be mounted under the barrel of many rifles.  Accepts RMSA10 box magazines."
+      }
+    ],
+    "weight": "1140 g",
+    "volume": "750 ml",
+    "longest_side": "380 mm",
+    "price": "1 kUSD 200 USD",
+    "price_postapoc": "50 USD",
+    "install_time": "5 m",
+    "material": [ "superalloy", "ceramic" ],
+    "symbol": ":",
+    "color": "dark_gray",
+    "location": "underbarrel",
+    "blacklist_mod": [ "knife_combat_army", "knife_combat", "enfield_bayonet", "knife_combat_marine", "makeshift_bayonet", "sword_bayonet" ],
+    "mod_targets": [ "rifle", "crossbow" ],
+    "gun_data": { "barrel_length": "419 mm", "ammo": "20x66mm", "skill": "shotgun", "dispersion": 320, "durability": 9, "reload": 125 },
+    "min_skills": [ [ "weapon", 2 ], [ "shotgun", 2 ] ],
+    "flags": [ "WATERPROOF_GUN", "NEVER_JAMS" ],
+    "pocket_data": [ { "pocket_type": "MAGAZINE_WELL", "item_restriction": [ "20x66_10_mag" ] } ]
+  },
+  {
+    "id": "rm121aux_mod",
+    "copy-from": "rm121aux",
+    "type": "GUNMOD",
+    "name": { "str": "modified RM121 aux shotgun" },
+    "description": "The Rivtech RM121 auxiliary weapon system is a magazine-fed semi-automatic caseless shotgun, which can be mounted under the barrel of many rifles.  Accepts RMSA10 box magazines.  This one was modified and customized to mount on pretty much any weapon other than pistols, if you so want.",
+    "mod_targets": [ "smg", "rifle", "shotgun", "launcher", "crossbow" ]
   }
 ]
diff --git a/data/json/recipes/weapon/mods.json b/data/json/recipes/weapon/mods.json
index 5ca0b3d996e93..ac7cdde466683 100644
--- a/data/json/recipes/weapon/mods.json
+++ b/data/json/recipes/weapon/mods.json
@@ -258,20 +258,6 @@
     "tools": [ [ [ "large_repairkit", 50 ], [ "small_repairkit", 100 ] ] ],
     "components": [ [ [ "m26_mass", 1 ] ], [ [ "scrap", 3 ] ], [ [ "plastic_chunk", 1 ] ] ]
   },
-  {
-    "result": "rm121aux_mod",
-    "type": "recipe",
-    "activity_level": "MODERATE_EXERCISE",
-    "category": "CC_*",
-    "subcategory": "CSC_*_NESTED",
-    "skill_used": "fabrication",
-    "difficulty": 7,
-    "skills_required": [ [ "gun", 2 ], [ "shotgun", 2 ] ],
-    "time": "90 m",
-    "autolearn": true,
-    "tools": [ [ [ "large_repairkit", 50 ], [ "small_repairkit", 100 ] ] ],
-    "components": [ [ [ "rm121aux", 1 ] ], [ [ "scrap", 3 ] ], [ [ "plastic_chunk", 1 ] ] ]
-  },
   {
     "result": "u_shotgun_mod",
     "type": "recipe",
diff --git a/data/mods/Magiclysm/Spells/attunements/Magnetism_Mage.json b/data/mods/Magiclysm/Spells/attunements/Magnetism_Mage.json
index 72acd8db152a6..0687132fd9a89 100644
--- a/data/mods/Magiclysm/Spells/attunements/Magnetism_Mage.json
+++ b/data/mods/Magiclysm/Spells/attunements/Magnetism_Mage.json
@@ -31,7 +31,6 @@
         [ "reloaded_10mm_fmj", 1 ],
         [ "12mm", 1 ],
         [ "reloaded_10mm_fmj", 1 ],
-        [ "20x66_slug", 1 ],
         [ "22_cb", 1 ],
         [ "22_fmj", 1 ],
         [ "22_lr", 1 ],
diff --git a/data/mods/TEST_DATA/item_demographics.json b/data/mods/TEST_DATA/item_demographics.json
index b654ad83dacfa..d8533f5d591f6 100644
--- a/data/mods/TEST_DATA/item_demographics.json
+++ b/data/mods/TEST_DATA/item_demographics.json
@@ -441,23 +441,6 @@
           "weight": 1,
           "items": { "bp_10mm_fmj": 1, "matchhead_10mm_fmj": 1, "10mm reloaded_10mm_fmj": 1 }
         },
-        {
-          "type": "20x66mm",
-          "weight": 1,
-          "items": {
-            "20x66_beanbag": 1,
-            "20x66_bootleg_flechette": 1,
-            "20x66_bootleg_shot": 1,
-            "20x66_bootleg_slug": 1,
-            "20x66_exp": 1,
-            "20x66_flare": 1,
-            "20x66_flechette": 1,
-            "20x66_frag": 1,
-            "20x66_inc": 1,
-            "20x66_shot": 1,
-            "20x66_slug": 1
-          }
-        },
         { "type": "300", "weight": 1, "items": { "300_winmag": 1, "bp_300_winmag": 1, "reloaded_300_winmag": 1 } },
         {
           "type": "303",
@@ -892,9 +875,6 @@
           "type": "other",
           "weight": 114,
           "items": {
-            "rm120c": 1,
-            "rm20": 1,
-            "rm228": 1,
             "m2010": 1,
             "weatherby_5": 1,
             "win70": 1,
@@ -1025,7 +1005,6 @@
             "raging_bull": 1,
             "remington_870_breacher": 1,
             "rm103a_pistol": 1,
-            "rm228": 1,
             "ruger_57": 1,
             "ruger_charger": 1,
             "ruger_charger_auto": 1,
@@ -1262,10 +1241,6 @@
             "remington_870": 1,
             "remington_870_express": 1,
             "revolver_shotgun": 1,
-            "rm120c": 1,
-            "rm121aux": 1,
-            "rm121aux_mod": 1,
-            "rm20": 1,
             "saiga_12": 1,
             "saiga_410": 1,
             "shotgun_410": 1,