Anyone with a Sig 556 notice how this thing mangles brass and ejects into the next county like no other?
I bought a 10" Sig 556 pistol about 6 months ago with the intent on creating an SBR when the paper work came through. Took it out to the range for the first time and was quite surprised to see the ejection pattern on the rifle was at about 1:30-2:00 and over 40’. Taking a look at some of the fired brass, I also noticed that the necks were crushed, bodies dented in the middle, and that brass was hitting the ejector so hard, it was splitting the case rims. Bottom line: the rifle seemed horribly overgassed. I read about similar issues from numerous members on a few different Sig forums.
I decided to take on the project of re-calibrating the ports on the gas valve in order to settle things down. It took me about 8 weeks (with help from a few members with testing), but the improved gas ports made a significant difference. Recoil is much softer (the bolt carrier is no longer hammering into the lower receiver at full speed), ejection is back to about 15’, and the brass is undamaged (big smiles for those of us who reload). It also becomes a viable option for those who run a suppressor on their Sig (adding a suppressor makes the already overgassed system even worse).
It is possible to modify the rifle’s stock valve and you can even pick up a Swiss SAN import valve as a spare to use as a donor.
this is basically just a re drilled gas valve. the op picked up a batch of swiss valves and re drilled the opposite side with new sized gas ports. he had tooling set up for a few different sized ports and notched the gas valve for the detent so it could be used rotated 180 degrees. basically you now have a 4 position gas valve. i believe he would also re drill your stock gas valve to a 4 position with your choice of gas port sizes. there were a couple of threads on tos and sigarms about it. i picked up a redrilled swiss valve for my 556 to help with the gas shooting suppressed. even with the smallest gas port offered my sig is one gassy bitch to shoot with a can. the action is noticeably smoother and less violent though. i haven’t separated any of my brass that i’ve shot with the new gas valve but just from shooting the gun and feeling the difference in the action and perceived recoil i would say the pics of the brass in the original post illustrate the difference with the smaller gas ports pretty well. i’ll try to get some pics of my gas valve and post them as soon as i can.
here are a few pics of the gas valve , it’s a bit dirty as i haven’t cleaned it since installing it. i’ve thought about welding up the largest hole to have an “off” position.
