and done!

code/modules/cm_marines/equipment/guncases.dm

@@ -93,6 +93,17 @@
 	new /obj/item/ammo_magazine/rifle/m41aMK1/ap(src)
 	new /obj/item/ammo_magazine/rifle/m41aMK1/ap(src)
 
+/obj/item/storage/box/guncase/m41aMK1/carbine
+	name = "\improper XM43A pulse carbine case"
+	desc = "Contains an unloaded XM43A pulse carbine and three 99 round clips."
+	storage_slots = 4
+	can_hold = list(/obj/item/weapon/gun/rifle/m41aMK1/carbine, /obj/item/ammo_magazine/rifle/m41aMK1)
+
+/obj/item/storage/box/guncase/m41aMK1/carbine/fill_preset_inventory()
+	new /obj/item/weapon/gun/rifle/m41aMK1/carbine(src)
+	new /obj/item/ammo_magazine/rifle/m41aMK1(src)
+	new /obj/item/ammo_magazine/rifle/m41aMK1(src)
+
 //------------
 //M79 grenade launcher
 /obj/item/storage/box/guncase/m79

code/modules/projectiles/gun_attachables.dm

@@ -3303,6 +3303,12 @@ Defined in conflicts.dm of the #defines folder.
 	scatter_unwielded_mod = -SCATTER_AMOUNT_TIER_9
 	accuracy_unwielded_mod = HIT_ACCURACY_MULT_TIER_1
 
+/obj/item/attachable/lasersight/carbine
+	name = "XM43A carbine underbarrel laser module"
+	desc = "What in god's name is this doing off the gun?"
+	icon_state = "lasersight"
+	attach_icon = "carbine_laser_a"
+
 /obj/item/attachable/lasersight/upp
 	name = "Zvezda Laser Module"
 	desc = "Visible band 512nm green laser, compatible with NVG and IR. Bears striking resemblance to an old Weyland Yutani offering... Decreases scatter, especially onehanded, slightly boosts accuracy. "

code/modules/projectiles/guns/rifles.dm

@@ -446,7 +446,37 @@
 	icon_state = "xm43a"
 	item_state = "xm43a"
 	current_mag = /obj/item/ammo_magazine/rifle/m41aMK1
-	starting_attachment_types = list(/obj/item/attachable/stock/rifle/collapsible, /obj/item/attachable/under/carbine_laser)
+	starting_attachment_types = list(/obj/item/attachable/stock/rifle/collapsible, /obj/item/attachable/lasersight/carbine)
+	aim_slowdown = SLOWDOWN_ADS_QUICK_MINUS
+	wield_delay = WIELD_DELAY_MIN
+	attachable_allowed = list(
+		/obj/item/attachable/stock/rifle/collapsible,
+		/obj/item/attachable/lasersight/carbine,
+	)
+
+/obj/item/weapon/gun/rifle/m41aMK1/carbine/handle_starting_attachment()
+	..()
+	var/obj/item/attachable/lasersight/carbine/S = new(src)
+	S.hidden = FALSE
+	S.flags_attach_features &= ~ATTACH_REMOVABLE
+	S.Attach(src)
+	update_attachable(S.slot)
+
+/obj/item/weapon/gun/rifle/m41aMK1/carbine/set_gun_config_values()
+	..()
+	set_fire_delay(FIRE_DELAY_TIER_11)
+	set_burst_amount(BURST_AMOUNT_TIER_4)
+	set_burst_delay(FIRE_DELAY_TIER_11)
+	accuracy_mult = BASE_ACCURACY_MULT
+	accuracy_mult_unwielded = BASE_ACCURACY_MULT - HIT_ACCURACY_MULT_TIER_4
+	scatter = SCATTER_AMOUNT_TIER_7
+	burst_scatter_mult = SCATTER_AMOUNT_TIER_9
+	scatter_unwielded = SCATTER_AMOUNT_TIER_3
+	damage_mult = BASE_BULLET_DAMAGE_MULT
+	recoil_unwielded = RECOIL_AMOUNT_TIER_4
+
+/obj/item/weapon/gun/rifle/m41aMK1/carbine/unloaded
+	current_mag = null
 
 //----------------------------------------------
 //Special gun for the CO to replace the smartgun