Sig556 Gas Valves

[Bret]

I shot my Sig 556 SBR with its original gas valve (marked E opposite UP designation) and the new gas valve (no letter designation opposite UP designation). Oddly enough, the new gas valve didn't seem to toss the cases shorter distances. With either installed, the cases went about 30 feet, +- 5 feet. That leads me to conclude that it's still over gassed even when using the 0.047" diameter gas hole. The only thing that I can think to do at this point is to weld up the holes and redrill them smaller.

[the_1iviper]

i believe the smallest port on my gas valve is drilled at .035 , i can't remember. this was meant for a suppressor setting but it still runs the gun fine without a can. i would like to go with a smaller gas port for a suppressed setting but don't have access to bits that small.

i believe .047 is the gas port size of the SAN 553 gas valve for the "normal" setting , i think the "adverse" port is .051. if it's a 4 setting valve i think the suppressed gas port is .031 with the 4th position being "off" on a SAN 553 valve.

if you have access to bits that small i would start out somewhere between .031 and .035 and see how it runs. i would like to weld and re drill one of my larger ports to .025~.026 to try out for a suppressed setting. also you can notch the opposite side of the gas valve to catch the detent and make a 4 position valve.

[Bret]

I know this is an old thread, but there's actually an update to this multiyear quest to find gas valves. Pierce Precision Engineering is now making 6-position Sig 550/551/556/751 gas valves. I bought a couple and they appear very well made. I installed one in my 556 and another in my 751. Both fit and rotated properly without any issues. I'll report back when I have a chance to test fire.
https://www.pierceprecisioneng.com/products


In the picture below, the top one is the Pierce Precision and the bottom one is the Sig factory.


The port sizes are as follows:
Port 1, 1.6mm
Port 2, 1.3mm
Port 3, 1.2mm
Port 4, 1.1mm
Port 5, 1.0 mm
Port 6, 0.9mm

Here's the Swiss gas valve chart for reference:

[MadAngler1]

I know this is an old thread, but there's actually an update to this multiyear quest to find gas valves. Pierce Precision Engineering is now making 6-position Sig 550/551/556/751 gas valves. I bought a couple and they appear very well made. I installed one in my 556 and another in my 751. Both fit and rotated properly without any issues. I'll report back when I have a chance to test fire.
https://www.pierceprecisioneng.com/products


In the picture below, the top one is the Pierce Precision and the bottom one is the Sig factory.


The port sizes are as follows:
Port 1, 1.6mm
Port 2, 1.3mm
Port 3, 1.2mm
Port 4, 1.1mm
Port 5, 1.0 mm
Port 6, 0.9mm

Here's the Swiss gas valve chart for reference:

Thanks Bret. I’ll check it out. What guns are you running these on?

It’s a shame that gas valves won’t count towards 922R, only gas pistons, per the list I have from a 553R letter Grant (Wes) submitted years ago.

[Bret]

I'll try them on my 550, 551, 556 Classic and 556 Classic SBR. I have two now, but will get as many as needed if they're benefitial. I know for sure that one will be beneficial on my 556 Classic SBR since it tosses the spent cases into orbit. I wish they made the smaller valves for the 552 and 553, but they don't (yet). I also got a valve for my Daewoo AR-100.

[SteyrAUG]

I know this is an old thread, but there's actually an update to this multiyear quest to find gas valves. Pierce Precision Engineering is now making 6-position Sig 550/551/556/751 gas valves. I bought a couple and they appear very well made. I installed one in my 556 and another in my 751. Both fit and rotated properly without any issues. I'll report back when I have a chance to test fire.
https://www.pierceprecisioneng.com/products


In the picture below, the top one is the Pierce Precision and the bottom one is the Sig factory.


The port sizes are as follows:
Port 1, 1.6mm
Port 2, 1.3mm
Port 3, 1.2mm
Port 4, 1.1mm
Port 5, 1.0 mm
Port 6, 0.9mm

Here's the Swiss gas valve chart for reference:

Given that the 751 is actually Swiss, wondering why you changed the gas valve?

[Bret]

Given that the 751 is actually Swiss, wondering why you changed the gas valve?

It's the same reason I'd change the gas valve on the 550, 551 or 556. They're all over gassed, though I'll have to verify the 751. I understand why Swiss Arms over gasses their rifles. They need to make sure that they run 100% in any environment and their army can't trust soldiers to properly tune the gas systems. They're less concerned about wear on the system. All that doesn't apply to me. I live in a warmer environment, want to reduce recoil and wear on the system, would like to use a suppressor and would like to reload the spent cases.

[SteyrAUG]

It's the same reason I'd change the gas valve on the 550, 551 or 556. They're all over gassed, though I'll have to verify the 751. I understand why Swiss Arms over gasses their rifles. They need to make sure that they run 100% in any environment and their army can't trust soldiers to properly tune the gas systems. They're less concerned about wear on the system. All that doesn't apply to me. I live in a warmer environment, want to reduce recoil and wear on the system, would like to use a suppressor and would like to reload the spent cases.

That tracks. I knew there were QC issues on the 556 where in some cases both gas settings were identical, so I understood why somebody might replace those but didn't think about somebody fine tuning a Swiss rifle.

[MadAngler1]

That tracks. I knew there were QC issues on the 556 where in some cases both gas settings were identical, so I understood why somebody might replace those but didn't think about somebody fine tuning a Swiss rifle.

I find the standard gas setting on my 551’s to be fine (both are 2022 made JDI imports). I do not run them suppressed though.

For the 553R I own, I’m interested in a setting with a larger hole for use with Hornady Subsonics. My 553R starts having hiccups on 1.2 and 1.3 settings. I use an OSS/HUX-WRX can though, not a baffled can. On 1.4-1.5, the 553R runs great and gives me a standard AK pattern ejection with brass and high quality steel cased (read: not Tula).

I have not shot my 550s yet. No time due to work.

[Bret]

For the 553R I own, I’m interested in a setting with a larger hole for use with Hornady Subsonics. My 553R starts having hiccups on 1.2 and 1.3 settings. I use an OSS/HUX-WRX can though, not a baffled can. On 1.4-1.5, the 553R runs great and gives me a standard AK pattern ejection with brass and high quality steel cased (read: not Tula).

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.