Sig556 Gas Valves

[Bret]

I ran a test today to compare the factory gas valve from my 556 Classic SBR to the Pierce Precision Engineering gas valve. Ammunition used was IMI M193 55gr FMJ.

I started out with the factory gas valve on the standard setting. The hole measures 0.047" (1.19mm). The five spent cases ejected an average of 31'.

I then installed the PPE gas valve and set it to port 5 which is the second from the smallest. The hole measures 0.039" (0.99mm). The five spend cases ejected an average of 16'

I then rotated the PPE gas valve to port 6 which is the smallest. The hole measures 0.034" (0.86mm). The five spent cases ejected an average of 6', but none of the next cartridges fed.

I then rotated the PPE gas valve back to port 5 and fired five more cartridges to verify reliability. Function was 100%.

The spent cases from cartridges fired using the factory gas valve have significant dents in their sides and some of the case mouths. Those from when the PPE gas valve was used look nearly perfect. I couldn't be happier with the PPE gas valve. If Sig had made a gas valve with the same setting, I think it would have had a significant impact on the rifle's reputation.

[SteyrAUG]

I ran a test today to compare the factory gas valve from my 556 Classic SBR to the Pierce Precision Engineering gas valve. Ammunition used was IMI M193 55gr FMJ.

I started out with the factory gas valve on the standard setting. The hole measures 0.047" (1.19mm). The five spent cases ejected an average of 31'.

I then installed the PPE gas valve and set it to port 5 which is the second from the smallest. The hole measures 0.039" (0.99mm). The five spend cases ejected an average of 16'

I then rotated the PPE gas valve to port 6 which is the smallest. The hole measures 0.034" (0.86mm). The five spent cases ejected an average of 6', but none of the next cartridges fed.

I then rotated the PPE gas valve back to port 5 and fired five more cartridges to verify reliability. Function was 100%.

The spent cases from cartridges fired using the factory gas valve have significant dents in their sides and some of the case mouths. Those from when the PPE gas valve was used look nearly perfect. I couldn't be happier with the PPE gas valve. If Sig had made a gas valve with the same setting, I think it would have had a significant impact on the rifle's reputation.

So you turned your SIG into a FAL? Seriously sounds like you got the fine tune rifle you were looking for.

[Bret]

So you turned your SIG into a FAL?

Basically, but the gas valve is easier to adjust and it doesn't weigh as much.

[MadAngler1]

Unsuppressed, I had to run my 553R on the 1.4 and 1.3 when I first shot it. It then must have loosened up some because it runs 100% on the 1.2 setting now with ejection about 10yds. This is with Tula and Wolf FMJ copper jacket. It's odd that you'd need a larger hole to run a subsonic. If anything, you'd think it would need to be smaller due to the increased back pressure.

Subsonic ammo needs more gas. It will have less back pressure. I am also using a HUX WRX OSS suppressor, so unlike my Surefire equipped Galil ACE, I won’t have the added back pressure of the suppressor to help with cycling subsonic ammo.

I emailed the company, and he does not currently make a 553R compatible valve. The 553R apparently has a different gas piston diameter from the 550/551/556 and 5.56 NATO 553s out there unfortunately.

I will stick with the Swiss made 550/551 gas valves for my 550/551 variants. I am not having any over gassing issues relatively speaking with the standard gas port sizes. I guess I can buy another spare 553R valve and do an experiment on one of the valve ports. I think a 1.8-2 mm port size might cycle subsonic ammo. 7.62x39 Subsonic is pretty darn sweet. I can get it to run in my Galil ACE, but only when I crank open the KNS piston all the way.

[Bret]

Subsonic ammo needs more gas. It will have less back pressure. I am also using a HUX WRX OSS suppressor, so unlike my Surefire equipped Galil ACE, I won’t have the added back pressure of the suppressor to help with cycling subsonic ammo.

That makes sense. My brain was assuming an installed suppressor increasing the back pressure.

I emailed the company, and he does not currently make a 553R compatible valve. The 553R apparently has a different gas piston diameter from the 550/551/556 and 5.56 NATO 553s out there unfortunately.

I'm pretty sure that the 552 and 553 have the smaller diameter gas valve as well.