Uppercases slot defines.

code/modules/projectiles/guns/energy/laser.dm

@@ -79,7 +79,7 @@
 	w_class = WEIGHT_CLASS_BULKY
 	force = 10
 	flags_1 =  CONDUCT_1
-	slot_flags = SLOT_BACK
+	slot_flags = ITEM_SLOT_BACK
 	ammo_type = list(/obj/item/ammo_casing/energy/laser/accelerator)
 	pin = null
 	ammo_x_offset = 3

code/modules/projectiles/guns/energy/pulse.dm

@@ -7,7 +7,7 @@
 	force = 10
 	modifystate = TRUE
 	flags_1 =  CONDUCT_1
-	slot_flags = SLOT_BACK
+	slot_flags = ITEM_SLOT_BACK
 	ammo_type = list(/obj/item/ammo_casing/energy/laser/pulse, /obj/item/ammo_casing/energy/electrode, /obj/item/ammo_casing/energy/laser)
 	cell_type = "/obj/item/stock_parts/cell/pulse"
 
@@ -39,7 +39,7 @@
 	name = "pulse carbine"
 	desc = "A compact variant of the pulse rifle with less firepower but easier storage."
 	w_class = WEIGHT_CLASS_NORMAL
-	slot_flags = SLOT_BELT
+	slot_flags = ITEM_SLOT_BELT
 	icon_state = "pulse_carbine"
 	item_state = null
 	cell_type = "/obj/item/stock_parts/cell/pulse/carbine"
@@ -54,7 +54,7 @@
 	name = "pulse pistol"
 	desc = "A pulse rifle in an easily concealed handgun package with low capacity."
 	w_class = WEIGHT_CLASS_SMALL
-	slot_flags = SLOT_BELT
+	slot_flags = ITEM_SLOT_BELT
 	icon_state = "pulse_pistol"
 	item_state = "gun"
 	cell_type = "/obj/item/stock_parts/cell/pulse/pistol"

code/modules/projectiles/guns/energy/special.dm

@@ -6,7 +6,7 @@
 	can_flashlight = 1
 	w_class = WEIGHT_CLASS_HUGE
 	flags_1 =  CONDUCT_1
-	slot_flags = SLOT_BACK
+	slot_flags = ITEM_SLOT_BACK
 	ammo_type = list(/obj/item/ammo_casing/energy/ion)
 	ammo_x_offset = 3
 	flight_x_offset = 17
@@ -20,7 +20,7 @@
 	desc = "The MK.II Prototype Ion Projector is a lightweight carbine version of the larger ion rifle, built to be ergonomic and efficient."
 	icon_state = "ioncarbine"
 	w_class = WEIGHT_CLASS_NORMAL
-	slot_flags = SLOT_BELT
+	slot_flags = ITEM_SLOT_BELT
 	pin = null
 	ammo_x_offset = 2
 	flight_x_offset = 18