I added an O-ring to the stock BCAR (Ok, “SCAR”) in the groove at the front. I think that's what it's there for. The cover then friction-fits over the stock BCAR. This is longer than the stock BCAR and will fit over and integrate well with the barrel cover from ASHprintingYT: https://www.printables.com/model/1363838-x-shot-motorized-piston-pump-barrel-cover
I recommend printing with an inside brim. This will be easier to remove than an outside brim. Test rings supplied for fitting over the BCAR body ("Tight" is TIGHT - let me know if you need a looser model).
Print in orange for outdoor play. I used PETG (PETG-CF Black and Elegoo Rapid Orange).
The author marked this model as their own original creation.