fix the issue seem ok to me after test

code/game/objects/items/storage/belt.dm

@@ -1452,6 +1452,7 @@
 	name = "\improper M276 pattern M82F flare gun holster rig"
 	desc = "The M276 is the standard load-bearing equipment of the USCM. It consists of a modular belt with various clips. This version is for the M82F flare gun."
 	storage_slots = 17
+	storage_holster = TRUE
 	max_storage_space = 20
 	icon_state = "m82f_holster"
 	item_state = "s_marinebelt"
@@ -1476,7 +1477,7 @@
 /obj/item/storage/belt/gun/flaregun/attackby(obj/item/W, mob/user)
 	if(istype(W, /obj/item/storage/box/m94))
 		var/obj/item/storage/box/m94/M = W
-		dump_ammo_into_belt_holster(M,user)
+		dump_into(M,user)
 	else
 		return ..()
 

code/game/objects/items/storage/storage.dm

@@ -30,7 +30,7 @@
 	var/list/content_watchers //list of mobs currently seeing the storage's contents
 	var/storage_flags = STORAGE_FLAGS_DEFAULT
 	var/has_gamemode_skin = FALSE ///Whether to use map-variant skins.
-	/// TRUE mean this belt as an holster for a gun. this variable is used for the dump into action.
+	var/storage_holster = FALSE
 
 /obj/item/storage/MouseDrop(obj/over_object as obj)
 	if(CAN_PICKUP(usr, src))
@@ -697,9 +697,7 @@ W is always an item. stop_warning prevents messaging. user may be null.**/
 	if(ammo_dumping.flags_magazine & AMMUNITION_HANDFUL_BOX)
 		var/handfuls = round(ammo_dumping.current_rounds / amount_to_dump, 1) //The number of handfuls, we round up because we still want the last one that isn't full
 		if(ammo_dumping.current_rounds != 0)
-
 			if(contents.len < storage_slots)
-
 				to_chat(user, SPAN_NOTICE("You start refilling [src] with [ammo_dumping]."))
 				if(!do_after(user, 1.5 SECONDS, INTERRUPT_ALL, BUSY_ICON_GENERIC)) return
 				for(var/i = 1 to handfuls)
@@ -723,46 +721,11 @@ W is always an item. stop_warning prevents messaging. user may be null.**/
 			to_chat(user, SPAN_WARNING("[ammo_dumping] is empty."))
 	return TRUE
 
-/obj/item/storage/proc/dump_ammo_into_belt_holster(obj/item/ammo_magazine/ammo_dumping, mob/user, amount_to_dump = 5) //amount_to_dump should never actually need to be used as default value
-	if(user.action_busy)
-		return
-
-	if(ammo_dumping.flags_magazine & AMMUNITION_CANNOT_REMOVE_BULLETS)
-		to_chat(user, SPAN_WARNING("You can't remove ammo from \the [ammo_dumping]!"))
-		return
-
-	if(ammo_dumping.flags_magazine & AMMUNITION_HANDFUL_BOX)
-		var/handfuls = round(ammo_dumping.current_rounds / amount_to_dump, 1) //The number of handfuls, we round up because we still want the last one that isn't full
-		if(ammo_dumping.current_rounds != 0)
-
-			if(contents.len < (storage_slots - 1))
-
-				to_chat(user, SPAN_NOTICE("You start refilling [src] with [ammo_dumping]."))
-				if(!do_after(user, 1.5 SECONDS, INTERRUPT_ALL, BUSY_ICON_GENERIC)) return
-				for(var/i = 1 to handfuls)
-					if(contents.len < (storage_slots - 1))
-						//Hijacked from /obj/item/ammo_magazine/proc/create_handful because it had to be handled differently
-						//All this because shell types are instances and not their own objects :)
-
-						var/obj/item/ammo_magazine/handful/new_handful = new /obj/item/ammo_magazine/handful
-						var/transferred_handfuls = min(ammo_dumping.current_rounds, amount_to_dump)
-						new_handful.generate_handful(ammo_dumping.default_ammo, ammo_dumping.caliber, amount_to_dump, transferred_handfuls, ammo_dumping.gun_type)
-						ammo_dumping.current_rounds -= transferred_handfuls
-						handle_item_insertion(new_handful, TRUE,user)
-						update_icon(-transferred_handfuls)
-					else
-						break
-				playsound(user.loc, "rustle", 15, TRUE, 6)
-				ammo_dumping.update_icon()
-			else
-				to_chat(user, SPAN_WARNING("[src] is full."))
-		else
-			to_chat(user, SPAN_WARNING("[ammo_dumping] is empty."))
-	return TRUE
-
-
-
 /obj/item/storage/proc/dump_into(obj/item/storage/M, mob/user)
+	if(storage_holster == TRUE && contents.len >= (storage_slots-1))
+		to_chat(user, SPAN_WARNING("[src] is full."))
+		return FALSE
+
 	if(user.action_busy)
 		return
 
@@ -777,6 +740,8 @@ W is always an item. stop_warning prevents messaging. user may be null.**/
 	if(!do_after(user, 1.5 SECONDS, INTERRUPT_ALL, BUSY_ICON_GENERIC))
 		return
 	for(var/obj/item/I in M)
+		if(storage_holster == TRUE && contents.len >= (storage_slots-1))
+			break
 		if(!has_room(I))
 			break
 		M.remove_from_storage(I)