I have a 6mm ARC upper i bought from Stag and shot it all last year with a carbine lower I built years ago for my .223. Long story short it shot great but i wanted to build another lower dedicated for the Arc. I used a a stag stripped lower and used a rifle length stock and buffer system. I went to the range and the POI of impact shifted over 3' and i ran out if adjustment on my scope, I put on my other lower and it shot where it always had. I did notice the buffer retainer pin doesnt catch the buffer all that well and when i opened to the lower the buffer came out and deadheaded against the hammer of the trigger group. I used the Magpul MOE stock and a basic buffer and i believe a tubbs rifle buffer spring. Any thoughts as to why is has such an impact change between the lowers?
