i attempted to build my first .308 and decided to use all dpms parts for availability. i bought the lar .308 upper at knob creek. i bought the lower at a gun shop and got the lower guts, buffer, tube, and spring from brownells. i assembled it and it looked right until working the bolt group. the bolt group will not go back far enough for the bolt catch to work. the bolt group goes back just the front of the bolt group and not the bolt for it to lock properly. i used the .308 buttstock kit from brownells and contacted their tech staff. i am a big fan of brownells but i think i stumped them. to experiment, i put a short carbine buffer in the tube and it locked up when i pressed the catch and worked with an empty mag. could i have used the wrong buffer tube for length?? i have the correct buffer for .308 and the correct spring (i hope!!) all advice, ribbing, and constructive criticisms welcome.