I built a 9mm sbr several years ago that a co-worker recently saw and then decided he wanted one also. Problem is, he wants a .40 caliber ar. If I remember correctly...I used a dedicated hahn block with 5.56 bolt catch, DPMS style hammer, 9mm buffer and complete RRA 9mm upper with the necessary 9mm mags. What parts would be needed to build a .40 caliber ar?
RRA sells complete .40 uppers but I have never seen .40 mag blocks and/or magazines. I would assume you would use the same 9mm buffer and DPMS style trigger, but what about the other parts? Thanks for any help and adivce.
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