INTRO: I got my LMT 5.56 Piston Upper on 1-2-09.  I  had been wanting to try out the Piston AR’s but I was very skepticl about them.  I wanted a 5.56 upper to supplement my 6.8 SPC AR’s because shooting the 6.8 SPC was becoming expensive.  I never had any problems with my DI AR’s [...]