Took two of my new rifles out to try them and begin breaking them in: SIG 516 Ruger SR556c I didn't do a whole lot with the SIG, ( yet ) other than getting the small SIG red dot sighted in at 50 yds and running 120 rounds through it. Only issue I had was one of my P-mags would only feed one round at a time then no more. The mag also felt loose in the mag well. I tried it again later and had no further issues from it, though I did separate that particular mag from the rest for now. The other 5 P-mags performed perfectly. It also didn't do quite as good as the Ruger in the group dept, but that's most likely because of it's 1/7 twist compared to the Ruger's 1/9. I was shooting Remington 55gr .223 and Federal 55gr 5.56. I plan on installing a Wilson Combat TTU and some metal BUISs later down the road. Don't know what optic it'll end up with, either one of my ACOGs or Aimpoints. With the Ruger, I sighted in the Comp M4S at 50 yds and ran 280 rounds through it. I added the Grip Pod, Magpul CTR and a Wilson Combat TTU. I REALLY love that TTU! While I currently have the Aimpoint sitting on a GG&G cantilever mount, I'll probably put the LaRue mount back on so I can run my Aimpoint 3X with it in tandem.