I had to put a lighter spring in my total sized M16 A2 clone but it surely ran great. Tried once more Along with the eleven.5" Comando Colt upper. No dice. Ran 500 rounds of wolf through it these days. Didnt hurt the spring in the least. Reference listing entries https://rarebreedtrigger42969.activoblog.com/42257018/rumored-buzz-on-frt-trigger