I was running a 12.5 Criterion Core which was a great barrel but I wanted something a little less gassy with my Sierra 5. The Criterion was well gassed with a .066 gas port but I would occasionally get gassed out which is due more to the Sierra 5 than the barrel.

I decided to give the sionics a try after reading a bit about it, I ended up getting their gas block as well. After getting the barrel in I pin gauged the gas port to be about .051 (a .052 wouldn’t fit). At first I was thinking I was gonna have to adjust my buffer/spring set up (A5H2 w/ Super 42 spring). After test firing, I found I didn’t have to change anything and it runs like a champ. If I had a different can this may not apply but with the S5 it kicks steel out at 4:00, 223 power ammo out at 3:30/5:00 and full power 5.56 at 3:00/3:30.

Some things I noticed after about 200 rounds:

1) Mags/ammo stay a bit cleaner 2) Gas to the face is non existent (using a BCM MK2 charging handle) 3) recoil is extremely pleasant

I was able to shoot it at 50 yards today to see how would group. Optic was an Eotech and the gun was rested on bags. I tried it with IMI 77 grain and Winchester WWB 5.56. Ended up getting a 3/4” group with the 77s and 1.5” with the Winchester, not awful for no magnification. Yes I know it’s better to shoot 10 shot groups instead of 5 but this is what I got.

All in all I’m extremely pleased with this barrel and look forward to shooting it more.