restrict or vent?

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January 01, 2022, 05:09 PM
restrict or vent?
I was tinkering with a Superlative Arms adjustable short stroke piston system today, and noticed that restricting the gas flow to the point of proper function with a silencer attached was a lot gassier than using their vent function. I was using an H2 buffer and regular carbine spring. As I have postulated in other discussions, I believe that letting that gas out of the bore, and exhausting it to the atmosphere via an exhaust vent in the gas system, is a logical and effective approach to reducing gas blowback into the action and the shooter's face. I believe all operating systems can fall victim to this "bore exhaust", when a silencer is applied. In the instance of the short stroke situation I was presented with today, if other esteemed SIGforum members were given the same circumstance, would you be more likely to keep the gas restricted and use a different spring and/or buffer, in an effort to delay reward movement of the BCG, which would logically serve to push more gas out through the can, or vent as I did? I think retaining the normal reciprocating mass is a desirable aspect of venting, and I am not sure that you could add enough spring or buffer weight to mitigate the bore exhaust to the same extent as the vent. What say the suppressor gurus?
January 02, 2022, 09:57 AM
A couple more things worth mentioning, and a question...
I am using Winchester M193 ammo. My benchmark for determining if a gun is too gassy is a 12-shot, relatively rapid drill. If I can't make it through that drill without being compromised by the emissions, the current setup is unsatisfactory, as was the case with the restricted flow in the above post; I didn't make it more than halfway, before I was squinting for relief.

Question: In adjusting gas venting in any operating system, for use with a silencer, is it more logical to adjust for more venting, or earlier venting?
January 26, 2022, 11:42 AM
This video is a great example of what I am talking about...

Watch weapon at 6:00 and then at 15:00. Even with an adjustable gas system on a piston rifle, there is way more exhaust back into the receiver and the shooters face, from the bore. If the adjustability serves to vent more gas sooner, rather than restrict the gas flow acting on the piston from within the bore, there'd be less of that.
January 26, 2022, 08:43 PM
I have gone both ways, and prefer the restriction. Mostly because I can have three to ten types of ammo for a gun. I set the restriction at the mid point of running just about everything.


If I was persinickity enough to only have one or two types of ammo I use with that gun, I would go your bleed off route.

I will say, my 556R with nomad 30 and brake has very little gas in the face issues. i can usually get a mag off rapid fire with out my eyes going nuts.

My POF 556 rifle is not as forgiving, but instead of the 26/27 rounds with little adverse effect it is like 20.

I tend to do most all my rifle shooting outdoors. I have no idea how it would work indoors where there isn't really a wind to carry the gass away.
January 27, 2022, 05:08 AM
The same mid-point compromise can be applied to the venting technique too.

The 556R has the longer gas system, and is a piston gun to boot. I am not surprised it handles it well. I am assuming your POF is piston-driven as well, though likely a shorter distance from chamber to gas port, which would result in more discomfort. I find that short-stroke systems are a bit friendlier to the suppressed shooter than long-stroke, but the length of the system makes a big difference. Every system vents in different ways too; the location and style of vent can make a big difference in perceived gassiness.

It sounds like either you shoot enough with a can under enough different circumstances to recognize the negative effects of the silencer, or you and I share a sensitivity to silencer-related emissions. Either way, it's nice to know someone else out there is irritated by that stuff. or at least notices it.
January 27, 2022, 06:48 AM
My old sig 556 patrol swat was terrible with can or with out. 5 rounds and i was gassed out.

The 556r is a vast improvement. My pofs are piston 556 and 308. My assembled ar 15s in 556 and 300 are di.

They are set midway. As i said 99% of my shooting is put doors on my home range. I almost always have a breeze. I bet it would be different indoor.

The one that surprised me the most was the mpx carbine. It was as bad as the sig 556. 5 to 10 rounds right in the eye.. When i form 1'd it into an sbr, it was still bad. It wasnt untill i went with ilwt gas block and barrel that the gass lessoned so an acceptable level.

My kriss, bnt, ptr9kt, and even the ftm fm9 are good on gas in the face compared to the original mpx carbine

I'll ad as an edit that this is my main complaint about the dead air odessa. While it suppresses great, i have a suspicion that the over all diamater effects how much gas is directed back down the barrel.

If you are using all 11 sections it is terrible at blow back in the face. Not just the acrid ammonia, but stinging blow back. If you drop it down to 8 sections it is significantly less prone to severe blowback.

The optimal is 4 or 5 baffles on a fixed barrel gun like a 92, or 6 on a tilting barrel gun.
January 27, 2022, 07:03 AM
The 556R isn't an improvement, it's just a different gun shooting a different caliber. The Patrol models were not great configurations; they shouldn't have put a 16-inch barrel on the short gas system.

I have also heard that the MPX is especially terrible. Funny that they didn't prioritize silencer use.
January 27, 2022, 07:10 AM
Originally posted by KSGM:
The 556R isn't an improvement, it's just a different gun shooting a different caliber. The Patrol models were not great configurations; they shouldn't have put a 16-inch barrel on the short gas system.

I have also heard that the MPX is especially terrible. Funny that they didn't prioritize silencer use.

While mechanical lly not an improvement, the lack of gas floating your eyelids is.

The mpx carbine was shit with out a can. Couldnt drop a 30 round mag with out seeing green.