Guns can drop bullet casings x2

code/__DEFINES/conflict.dm

@@ -78,6 +78,10 @@
 #define GUN_SUPPORT_PLATFORM (1<<16)
 /// No gun description, only base desc
 #define GUN_NO_DESCRIPTION (1<<17)
+/// If it can automatically eject shell casings
+#define GUN_AUTO_EJECT_CASINGS (1<<18)
+/// If it needs to manually eject shell casings (like bolt actions)
+#define GUN_MANUAL_EJECT_CASINGS (1<<19)
 // NOTE: Don't add flags past 1<<23, it'll break things due to BYOND limitations. You can usually use a Component instead.
 
 #define USES_STREAKS (1<<0)

code/datums/ammo/ammo.dm

@@ -96,6 +96,9 @@
 	/// Whether or not this ammo ignores mobs that are lying down
 	var/hits_lying_mobs = FALSE
 
+	/// Type of empty shell casing
+	var/shell_casing
+
 /datum/ammo/New()
 	set_bullet_traits()
 

code/datums/ammo/bullet/lever_action.dm

@@ -14,6 +14,7 @@
 	accurate_range = 14
 	effective_range_max = 7
 	handful_state = "lever_action_bullet"
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/cartridge/lever_action
 
 //unused and not working. need to refactor MD code. Unobtainable.
 //intended mechanic is to have xenos hit with it show up very frequently on any MDs around

code/datums/ammo/bullet/pistol.dm

@@ -13,6 +13,7 @@
 	damage = 40
 	penetration= ARMOR_PENETRATION_TIER_2
 	shrapnel_chance = SHRAPNEL_CHANCE_TIER_2
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing
 
 /datum/ammo/bullet/pistol/setup_faction_clash_values()
 	. = ..()
@@ -107,6 +108,7 @@
 	hit_effect_color = "#00aeff"
 	stamina_damage = 30
 	accuracy = HIT_ACCURACY_TIER_4
+	shell_casing = null
 
 // Used by M1911 and KT-42
 /datum/ammo/bullet/pistol/heavy

code/datums/ammo/bullet/revolver.dm

@@ -10,6 +10,7 @@
 	damage = 72
 	penetration = ARMOR_PENETRATION_TIER_1
 	accuracy = HIT_ACCURACY_TIER_1
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing
 
 /datum/ammo/bullet/revolver/marksman
 	name = "marksman revolver bullet"
@@ -90,6 +91,7 @@
 	icon_state = "shrapnelshot"
 	handful_state = "shrapnel"
 	bonus_projectiles_type = /datum/ammo/bullet/revolver/upp/shrapnel_bits
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shrapnel
 
 	max_range = 6
 	damage = 40 // + TIER_4 * 3

code/datums/ammo/bullet/rifle.dm

@@ -17,6 +17,7 @@
 	effective_range_max = 7
 	damage_falloff = DAMAGE_FALLOFF_TIER_7
 	max_range = 24 //So S8 users don't have their bullets magically disappaer at 22 tiles (S8 can see 24 tiles)
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/cartridge
 
 /datum/ammo/bullet/rifle/holo_target
 	name = "holo-targeting rifle bullet"
@@ -222,7 +223,6 @@
 
 /datum/ammo/bullet/rifle/mar40
 	name = "heavy rifle bullet"
-
 	damage = 55
 
 /datum/ammo/bullet/rifle/type71

code/datums/ammo/bullet/shotgun.dm

@@ -6,6 +6,7 @@
 
 /datum/ammo/bullet/shotgun
 	headshot_state = HEADSHOT_OVERLAY_HEAVY
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell // safe to assume that most shotguns will have a casing
 
 /datum/ammo/bullet/shotgun/setup_faction_clash_values()
 	. = ..()
@@ -23,6 +24,7 @@
 	accuracy = HIT_ACCURACY_TIER_3
 	damage_armor_punch = 2
 	handful_state = "slug_shell"
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/green_shell
 
 /datum/ammo/bullet/shotgun/slug/on_hit_mob(mob/M,obj/projectile/P)
 	knockback(M, P, 6)
@@ -53,6 +55,7 @@
 	damage = 60
 	penetration = ARMOR_PENETRATION_TIER_8
 	accuracy = HIT_ACCURACY_TIER_5
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/es7_slug
 
 /datum/ammo/bullet/shotgun/beanbag
 	name = "beanbag slug"
@@ -69,6 +72,7 @@
 	accuracy = HIT_ACCURACY_TIER_3
 	shell_speed = AMMO_SPEED_TIER_3
 	handful_state = "beanbag_slug"
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/blue_shell
 
 /datum/ammo/bullet/shotgun/beanbag/on_hit_mob(mob/M, obj/projectile/P)
 	if(!M || M == P.firer)
@@ -95,6 +99,7 @@
 	accuracy = HIT_ACCURACY_TIER_3
 	shell_speed = AMMO_SPEED_TIER_4
 	handful_state = "shock_slug"
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/es7_shock
 
 /datum/ammo/bullet/shotgun/beanbag/es7/on_hit_mob(mob/mobs, obj/projectile/P)
 	if(!isyautja(mobs) && !isxeno(mobs))
@@ -117,6 +122,7 @@
 	damage = 55
 	penetration= ARMOR_PENETRATION_TIER_1
 	handful_state = "incendiary_slug"
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/incen_slug
 
 /datum/ammo/bullet/shotgun/incendiary/set_bullet_traits()
 	. = ..()
@@ -151,6 +157,7 @@
 	bonus_projectiles_amount = EXTRA_PROJECTILES_TIER_3
 	handful_state = "flechette_shell"
 	multiple_handful_name = TRUE
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/purple_shell
 
 /datum/ammo/bullet/shotgun/flechette/setup_faction_clash_values()
 	. = ..()
@@ -194,11 +201,13 @@
 	pen_armor_punch = 0
 	handful_state = "buckshot_shell"
 	multiple_handful_name = TRUE
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/red_shell
 
 /datum/ammo/bullet/shotgun/buckshot/incendiary
 	name = "incendiary buckshot shell"
 	handful_state = "incen_buckshot"
 	handful_type = /obj/item/ammo_magazine/handful/shotgun/buckshot/incendiary
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/incen_shell
 
 /datum/ammo/bullet/shotgun/buckshot/incendiary/set_bullet_traits()
 	. = ..()
@@ -263,6 +272,7 @@
 	shell_speed = AMMO_SPEED_TIER_2
 	damage_armor_punch = 0
 	pen_armor_punch = 0
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/heavy
 
 /datum/ammo/bullet/shotgun/heavy/buckshot/on_hit_mob(mob/M,obj/projectile/P)
 	knockback(M,P)
@@ -283,6 +293,7 @@
 	accurate_range = 3
 	max_range = 4
 	bonus_projectiles_type = /datum/ammo/bullet/shotgun/heavy/buckshot/dragonsbreath/spread
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/heavy/incen_shell
 
 /datum/ammo/bullet/shotgun/heavy/buckshot/dragonsbreath/set_bullet_traits()
 	. = ..()
@@ -307,6 +318,7 @@
 	damage = 90 //ouch.
 	penetration = ARMOR_PENETRATION_TIER_6
 	damage_armor_punch = 2
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/heavy/green_shell
 
 /datum/ammo/bullet/shotgun/heavy/slug/on_hit_mob(mob/M,obj/projectile/P)
 	knockback(M, P, 7)
@@ -340,6 +352,7 @@
 	stamina_damage = 100
 	accuracy = HIT_ACCURACY_TIER_2
 	shell_speed = AMMO_SPEED_TIER_2
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/heavy/blue_shell
 
 /datum/ammo/bullet/shotgun/heavy/beanbag/on_hit_mob(mob/M, obj/projectile/P)
 	if(!M || M == P.firer)
@@ -363,6 +376,7 @@
 	damage_var_high = PROJECTILE_VARIANCE_TIER_8
 	penetration = ARMOR_PENETRATION_TIER_10
 	bonus_projectiles_amount = EXTRA_PROJECTILES_TIER_2
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/heavy/purple_shell
 
 /datum/ammo/bullet/shotgun/heavy/flechette/setup_faction_clash_values()
 	. = ..()
@@ -394,6 +408,7 @@
 	handful_state = "breaching_shell"
 	multiple_handful_name = TRUE
 	bonus_projectiles_type = /datum/ammo/bullet/shotgun/light/breaching/spread
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/light
 
 	accuracy_var_low = PROJECTILE_VARIANCE_TIER_6
 	accuracy_var_high = PROJECTILE_VARIANCE_TIER_6
@@ -426,6 +441,7 @@
 	stamina_damage = 35
 	bonus_projectiles_amount = EXTRA_PROJECTILES_TIER_3
 	penetration = ARMOR_PENETRATION_TIER_1
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/light/rubbershot
 
 /datum/ammo/bullet/shotgun/light/rubber/spread
 	name = "additional rubber buckshot"
@@ -446,6 +462,7 @@
 	penetration = ARMOR_PENETRATION_TIER_3
 	damage_falloff = DAMAGE_FALLOFF_TIER_1 * 3 //It has a lot of energy, but the 26mm bullet drops off fast.
 	effective_range_max = EFFECTIVE_RANGE_MAX_TIER_2 //Full damage up to this distance, then falloff for each tile beyond.
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/shell/twobore_shell
 	var/hit_messages = list()
 
 /datum/ammo/bullet/shotgun/twobore/on_hit_mob(mob/living/M, obj/projectile/P)

code/datums/ammo/bullet/smg.dm

@@ -21,6 +21,7 @@
 	damage_falloff = DAMAGE_FALLOFF_TIER_5
 	scatter = SCATTER_AMOUNT_TIER_6
 	accuracy = HIT_ACCURACY_TIER_3
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing
 
 /datum/ammo/bullet/smg/m39
 	name = "high-velocity submachinegun bullet" //i don't want all smgs to inherit 'high velocity'

code/datums/ammo/bullet/sniper.dm

@@ -89,6 +89,7 @@
 	name = "crude sniper bullet"
 	damage = 42
 	penetration = ARMOR_PENETRATION_TIER_6
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/cartridge
 
 /datum/ammo/bullet/sniper/crude/on_hit_mob(mob/M, obj/projectile/P)
 	. = ..()
@@ -98,6 +99,7 @@
 	name = "armor-piercing sniper bullet"
 	damage = 80
 	penetration = ARMOR_PENETRATION_TIER_10
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/cartridge //traditionally, SVDs use casings
 
 /datum/ammo/bullet/sniper/anti_materiel
 	name = "anti-materiel sniper bullet"
@@ -107,6 +109,7 @@
 	damage = 125
 	shell_speed = AMMO_SPEED_TIER_6
 	penetration = ARMOR_PENETRATION_TIER_10 + ARMOR_PENETRATION_TIER_5
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/cartridge // I would be surprised if something as powerful as this would not need a casing
 
 /datum/ammo/bullet/sniper/anti_materiel/proc/stopping_power_knockback(mob/living/living_mob, obj/projectile/fired_projectile)
 	var/stopping_power = min(CEILING((fired_projectile.damage/30), 1), 5) // This is from bullet damage, and does not take Aimed Shot into account.
@@ -275,6 +278,7 @@
 	handful_state = "vulture_bullet"
 	sound_hit = 'sound/bullets/bullet_vulture_impact.ogg'
 	flags_ammo_behavior = AMMO_BALLISTIC|AMMO_SNIPER|AMMO_IGNORE_COVER|AMMO_ANTIVEHICLE
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/cartridge
 
 /datum/ammo/bullet/sniper/anti_materiel/vulture/on_hit_mob(mob/hit_mob, obj/projectile/bullet)
 	. = ..()
@@ -317,6 +321,7 @@
 	damage = 150
 	shell_speed = AMMO_SPEED_TIER_6 + AMMO_SPEED_TIER_2
 	penetration = ARMOR_PENETRATION_TIER_10 + ARMOR_PENETRATION_TIER_5
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/cartridge
 
 /datum/ammo/bullet/sniper/elite/set_bullet_traits()
 	. = ..()

code/datums/ammo/bullet/special_ammo.dm

@@ -242,6 +242,7 @@
 	accurate_range = 12
 	damage = 35
 	penetration = ARMOR_PENETRATION_TIER_6
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/cartridge
 
 /datum/ammo/bullet/minigun/New()
 	..()
@@ -266,6 +267,7 @@
 	damage = 45 //7.62x51 is scary
 	penetration= ARMOR_PENETRATION_TIER_6
 	shrapnel_chance = SHRAPNEL_CHANCE_TIER_2
+	shell_casing = /obj/effect/decal/cleanable/ammo_casing/cartridge
 
 /datum/ammo/bullet/pkp
 	name = "machinegun bullet"