I had to place a lighter spring in my whole sized M16 A2 clone but it ran great. Tried out once more with the eleven.5" Comando Colt upper. No dice. Ran 500 rounds of wolf through it now. Didnt harm the spring at all.However, we're in an ammo lack, so it isn't just like the $a hundred big difference is gonna make a dent from the expenditure which i