Adds several new back slot icons for guns, while also updating two ex…

…isting ones. (tgstation#47898)

* Adds back sprites for the Particle Acceleration Rifle, and updates the back sprites for the combat and riot shotguns.

* Adds adds a back slot icon for compact combat shotguns.

* Adds a back slot icon for the surplus rifle.

* Adds back slot icon for the Mosin Nagant and allows it to be worn on the back.

code/modules/projectiles/guns/ballistic/rifle.dm

@@ -56,7 +56,7 @@ obj/item/gun/ballistic/rifle/attackby(obj/item/A, mob/user, params)
 	weapon_weight = WEAPON_HEAVY
 	icon_state = "moistnugget"
 	item_state = "moistnugget"
-	slot_flags = 0 //no ITEM_SLOT_BACK sprite, alas
+	slot_flags = ITEM_SLOT_BACK
 	mag_type = /obj/item/ammo_box/magazine/internal/boltaction
 	can_bayonet = TRUE
 	knife_x_offset = 27
@@ -89,6 +89,7 @@ obj/item/gun/ballistic/rifle/attackby(obj/item/A, mob/user, params)
 	pin = /obj/item/firing_pin/magic
 	icon_state = "arcane_barrage"
 	item_state = "arcane_barrage"
+	slot_flags = null
 	can_bayonet = FALSE
 	item_flags = NEEDS_PERMIT | DROPDEL | ABSTRACT | NOBLUDGEON
 	flags_1 = NONE

code/modules/projectiles/guns/misc/beam_rifle.dm

@@ -24,6 +24,7 @@
 	ammo_x_offset = 3
 	ammo_y_offset = 3
 	modifystate = FALSE
+	charge_sections = 1
 	weapon_weight = WEAPON_HEAVY
 	w_class = WEIGHT_CLASS_BULKY
 	ammo_type = list(/obj/item/ammo_casing/energy/beam_rifle/hitscan)
@@ -70,9 +71,6 @@
 	var/current_zoom_x = 0
 	var/current_zoom_y = 0
 
-	var/static/image/charged_overlay = image(icon = 'icons/obj/guns/energy.dmi', icon_state = "esniper_charged")
-	var/static/image/drained_overlay = image(icon = 'icons/obj/guns/energy.dmi', icon_state = "esniper_empty")
-
 	var/datum/action/item_action/zoom_lock_action/zoom_lock_action
 	var/mob/listeningTo
 
@@ -148,14 +146,6 @@
 	current_zoom_x = 0
 	current_zoom_y = 0
 
-/obj/item/gun/energy/beam_rifle/update_icon()
-	cut_overlays()
-	var/obj/item/ammo_casing/energy/primary_ammo = ammo_type[1]
-	if(!QDELETED(cell) && (cell.charge >= primary_ammo.e_cost))
-		add_overlay(charged_overlay)
-	else
-		add_overlay(drained_overlay)
-
 /obj/item/gun/energy/beam_rifle/attack_self(mob/user)
 	projectile_setting_pierce = !projectile_setting_pierce
 	to_chat(user, "<span class='boldnotice'>You set \the [src] to [projectile_setting_pierce? "pierce":"impact"] mode.</span>")