Uppercases slot defines.

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

@@ -363,7 +363,7 @@
 	zoomable = TRUE
 	zoom_amt = 10 //Long range, enough to see in front of you, but no tiles behind you.
 	zoom_out_amt = 13
-	slot_flags = SLOT_BACK
+	slot_flags = ITEM_SLOT_BACK
 	actions_types = list()
 
 
@@ -393,7 +393,7 @@
 	can_unsuppress = TRUE
 	can_suppress = TRUE
 	w_class = WEIGHT_CLASS_HUGE
-	slot_flags = SLOT_BACK
+	slot_flags = ITEM_SLOT_BACK
 	actions_types = list()
 
 /obj/item/gun/ballistic/automatic/surplus/update_icon()

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

@@ -9,7 +9,7 @@
 	item_state = "backpack"
 	lefthand_file = 'icons/mob/inhands/equipment/backpack_lefthand.dmi'
 	righthand_file = 'icons/mob/inhands/equipment/backpack_righthand.dmi'
-	slot_flags = SLOT_BACK
+	slot_flags = ITEM_SLOT_BACK
 	w_class = WEIGHT_CLASS_HUGE
 	var/obj/item/gun/ballistic/minigun/gun
 	var/armed = 0 //whether the gun is attached, 0 is attached, 1 is the gun is wielded.
@@ -33,7 +33,7 @@
 /obj/item/minigunpack/attack_hand(var/mob/living/carbon/user)
 	if(src.loc == user)
 		if(!armed)
-			if(user.get_item_by_slot(slot_back) == src)
+			if(user.get_item_by_slot(SLOT_BACK) == src)
 				armed = 1
 				if(!user.put_in_hands(gun))
 					armed = 0

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

@@ -257,7 +257,7 @@
 	weapon_weight = WEAPON_MEDIUM
 	force = 10
 	flags_1 = CONDUCT_1
-	slot_flags = SLOT_BACK
+	slot_flags = ITEM_SLOT_BACK
 	mag_type = /obj/item/ammo_box/magazine/internal/shot/dual
 	sawn_desc = "Omar's coming!"
 	obj_flags = UNIQUE_RENAME
@@ -314,7 +314,7 @@
 	if(istype(A, /obj/item/stack/cable_coil) && !sawn_off)
 		var/obj/item/stack/cable_coil/C = A
 		if(C.use(10))
-			slot_flags = SLOT_BACK
+			slot_flags = ITEM_SLOT_BACK
 			to_chat(user, "<span class='notice'>You tie the lengths of cable to the shotgun, making a sling.</span>")
 			slung = TRUE
 			update_icon()
@@ -340,7 +340,7 @@
 	item_state = "gun"
 	w_class = WEIGHT_CLASS_NORMAL
 	sawn_off = TRUE
-	slot_flags = SLOT_BELT
+	slot_flags = ITEM_SLOT_BELT
 
 
 /obj/item/gun/ballistic/revolver/reverse //Fires directly at its user... unless the user is a clown, of course.

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

@@ -6,7 +6,7 @@
 	w_class = WEIGHT_CLASS_BULKY
 	force = 10
 	flags_1 =  CONDUCT_1
-	slot_flags = SLOT_BACK
+	slot_flags = ITEM_SLOT_BACK
 	mag_type = /obj/item/ammo_box/magazine/internal/shot
 	casing_ejector = FALSE
 	var/recentpump = 0 // to prevent spammage
@@ -107,7 +107,7 @@
 	desc = "This piece of junk looks like something that could have been used 700 years ago. It feels slightly moist."
 	icon_state = "moistnugget"
 	item_state = "moistnugget"
-	slot_flags = 0 //no SLOT_BACK sprite, alas
+	slot_flags = 0 //no ITEM_SLOT_BACK sprite, alas
 	mag_type = /obj/item/ammo_box/magazine/internal/boltaction
 	var/bolt_open = FALSE
 	can_bayonet = TRUE

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

@@ -73,7 +73,7 @@
 	item_state = "crossbow"
 	mag_type = /obj/item/ammo_box/magazine/internal/shot/toy/crossbow
 	fire_sound = 'sound/items/syringeproj.ogg'
-	slot_flags = SLOT_BELT
+	slot_flags = ITEM_SLOT_BELT
 	w_class = WEIGHT_CLASS_SMALL
 
 /obj/item/gun/ballistic/automatic/c20r/toy //This is the syndicate variant with syndicate firing pin and riot darts.