...Other than a silencer being of a certain design: conventional, LBP, or flow-through.

I have come to believe that a silencer's perceived performance, when it comes to "gassiness", is quite multi-faceted.

Obviously, the broad swath of potential hosts have all of their various performance idiosyncrasies.

The atmospherics on the particular day, or in the particular circumstance vary as well.

Things like the lubrication used in the firearm, and its overall cleanliness are contributing factors.

The ammunition used is big factor in any silencer performance evaluation. I think it may be bigger than we give it credit for.

Finally, things like the user's eye protection, rate of fire, etc.

We all often concede that we don't perform true comparative tests with silencers. Be it to evaluate noise, flash, gas, whatever. And, even if we think we are doing a strict test, we may still be missing something that could lead to a false impression of performance.

***Edited to add subjective shooter sensitivity, per Smudges reply below. Absolutely a critical factor I should've initially included.

This message has been edited. Last edited by: KSGM,

quote:

What influences "gassiness"?

First thing I thought of: Taco Bell

Indeed.

Honestly? I think it comes down more to the shooter and how sensitive they are to it than any of the above. Obviously, those all play a part, but I recently handed off my 9mm PCC setup to a buddy who put five rounds through it and turned to me and said "it's kinda gassy, isn't it?" His tone and body language indicated that it was extremely unpleasant for him, and he handed it back.

I was honestly astounded. I've only ever caught a few faint whiffs off gas from it, never in any amounts that would have me saying I think it's "gassy." I did some thinking about it. It's a traditional baffle style can, ten of them, and even range trips with maybe a hundred rounds or so result in that gun having fouling all over the outside of the lower, in the magazines, just everywhere. Maybe it is gassy, and maybe it just doesn't bother me.

I've only ever caught a few faint whiffs of gas off my Polonium on several hosts, and that's supposed to be a prime offender if the Reddit nerds are to be believed.

Maybe I'm just not at all sensitive to "gas." The only time I've been gassed out was shooting a Surefire RC2 on a Mk18 at an indoor range. I don't know how many rounds it took, but it wasn't a lot. That was maybe two years ago, and I'm pretty sure that was the last time I shot indoors, and haven't been gassed out since.

All that said, I'm probably going to pick up a reduced backpressure 9mm can next. Mainly, because I'm tired of how damned filthy my gun gets and I want to minimize the amount of shit blowing back into the action. I've actually been emailing back and forth with the guy at Stealth Additive Works about the 9mm cans he has in the works. They're not ready yet, and I didn't ask when or how much, but he has a 9mm can I'm very interested in. I told him that if it works the way his rifle can does, it's an instant buy for me. There are other new 3d printed titanium cans that are a little quieter, but so far, it's looking like he has the whole marked beat so far in terms of backpressure.

I don’t have any experience with rifle setups that are considered to be “gassy,” i.e., blow gas back at the shooter, but I suspect much of the reaction to a particular characteristic is driven by exposure and expectations. As someone who literally grew up through the period when full power 357 Magnum revolvers and 45 ACP 1911 pistols were common, I’m still a little bemused by the idea that the ferocious ( ) recoil of the 40 S&W cartridge was the reason for its demise. Once an idea takes hold in a particular culture or community, and just as believing is seeing, what we expect is what we experience.

Yeah, when I started in the suppressor thing, there was all this talk about tuning the gun to the can. I've talked with guys who, it seemed to me, went totally overboard in making sure that their rifle and particular ammo cycled the gun just the perfect amount. I installed the HBI gas plug in my Bren 2. It has three settings - low, medium, and high. On the low setting with my Polonium, it's perfect. Cycles reliably, and shoots really smooth. There is also the KNS "Czechvalve" which has forty two different settings. If you go to the Bren 2 subreddit, there are guys who will tell you it's basically required gear if you're going to shoot suppressed.

All I want is for my stuff to be quieter and not choke me on fumes. I don't need the perfect balance, I can accept that it's all tradeoffs. Smelling a bit of gas on strings of heavy fire seems to me to be a reasonable expectation.

The type of powder in the round can have a huge effect on it, also. The formulation influences the types of gaseous products produced and their quantities. The burn rate also makes noticeable differences.

Well, considering the price difference is a pretty-reasonable $50 between those two Bren valves, I can see where someone might opt for the "unlimited" adjustability for the extra $. Like you, I prefer the more KISS approach of three settings.

Forgive the rambling, putting a few thoughts down real quick;


The suppressor acts as a secondary pressure chamber. If it's still at an elevated pressure when the bolt unlocks and moves rearward gas will flow from both ends of the suppressor to attempt to reach equilibrium.

The quantity of gas working the action is derived from the port size, location on the barrel, and characteristics of the cartridge such as type and burn rate of the powder.

The pressure in the chamber spikes, and as the bullet is driven down the barrel the "chamber" (the vessel holding pressure) is expanding. At some point combustion ends and the amount of gas no longer increases, but the chamber volume continues to do so.

Gas flows from high pressure to low pressure. The speed of the gas is relative to the difference in pressure. So if you're at 20,000psi and the bullet passes the gas port in the barrel, you've got a hell of a lot of force acting to accelerate that gas, and containing it on the other end is a challenge - you'll want a minuscule gas port to create orifice pressure drop before that dumps downstream. Move the port forward 3" and triple the size of the chamber behind the bullet before it hits the gas block and now you have just under 7,000psi to do the same work - the gas port will need to be significantly bigger to do so. If the time it takes the bullet to leave the barrel after passing the gas port is shorter, you'll need the gas to work faster to stay within that time before the system is uncorked and you have another hole open to low pressure (atmosphere), and that means keeping the pressure up so you have velocity and energy at the back end of the system. And if the back end of the system, meaning the bolt carrier group and buffer and everything they touch during a recoil cycle, leaks like a sieve, you're going to need more gas to get the thing going. And any drag added either in component selection, tolerance, fit, lubrication/friction, the more gas you'll need. [numbers are all made up and just a representation without looking at drawings and doing real math]

Balancing that whole system is tricky. Throw in a whole lot of different manufacturers that operate a whole lot of philosophies on how to do it, how to improve it, what to improve, etc etc, and people throwing together homebrews, FFL builders, etc etc you get a whole lot of variation on how much gas comes out that ass.

For what it's worth - the current trend in "Flow" or LBP suppressors, as far as the companies making them using 3D printing and whatnot, they're able to simultaneously balance a lot of variables to make what is essentially a big diffuser tube whose goal it is to control exiting gas velocity. And it's done by using computational flow design (CFD) software to perform the engineering analysis. The better you are at modeling the blast of gasses exiting the barrel and manipulating geometry of an object that can be made on direct metal laser scintering (DMLS) additive machines, the better you can made a suppressor that performs as desired.

The OP was inspired by my recent experience with two different ammo types in the same silencer/host. One ammo performed MUCH differently, when it came to the perception of exhaust irritants.

Context of the graphic aside (this is from a Naval gun where they're varying big ol' piles of powder) - the pressure curve is different between loads. It changes how the gun behaves.

You can't precisely optimize for more than one load, unless the characteristics between them are tight.

this is not an actual contribution to the discussion, but simply an odd observation. I have a CZ Bren 2 that the gas piston allows a position of 'no gas'. What amazes me when I shoot it that way is that when you pull the bolt back there is literally no gas vented. like none. I fully get the the valve selection has shut off dumping it back into the receiver via the gas port, but I would have expected some residual in the barrel that would vent to the ejection port when you cycle the weapon.

The aspects touched-on by Rustpot seem to explain my experience, and the impact ammo can have on perceived gassiness.

I can tell you that using an adjustable gas block to dial back your gas when using a suppressor will greatly reduce gas to the face. On an AR platform.

quote:

Originally posted by IndianaBoy:
I can tell you that using an adjustable gas block to dial back your gas when using a suppressor will greatly reduce gas to the face. On an AR platform.

I am tempted to try one of the Riflespeed adjustable blocks on my SBR.

I have owned suppressors for many years, and there is only a single firearm I would describe as "gassy" even without a suppressor, and that was the Tavor. The gas vents are right next to the shooters face, which was an interesting (and poor) design choice.

Aside form that, there have been times when shooting various ARs when I've suddenly been gassed, but I would attribute those instances more to a breeze carrying it to my face than a particular setup/configuration of the weapon. It is also definitely more common when shooting cheaper ammunition, as some have pointed out. Steel cased ammunition does it more than any other to me.

One other interesting note is that people love to claim how gassy the MPX is. Ive owned both a Gen I and a Gen II and I have thought both of them were the most pleasant shooting suppressors firearms I have ever laid my hands on.

General rifle design, barrel length, gas port location, gas port size, suppressor design/build, and ammo all factor into the gas issues. But IMO the biggest factor is generally the shooter, and how he's shooting.

The gassiest gun I have by far is a 14.5" LWRC piston upper. Yeah that's right -- from a so-called high-end manufacturer, using a piston system that's not supposed be gassy. I notice the gas most during the first few shots of the day, especially after lubing, from a very stable shooting position, and while shooting slow & precision fire. Shooting quickly from an less stable position, run & gun, engaging multiple targets while on the clock -- what gas?

IMO the whole gas in the face issue is overblown. Yeah, pun intended. Same for the gas signature out the front of a suppressor. When a person really needs to shoot and when a person is really concentrating on the results, little things go by the wayside.

I've never noticed gas in competition, on the clock. Nor laying down in cactus. Nor cuts, scrapes, bruises, pulled muscles, insect bites, sunburn, dehydration, hunger, torn clothing, the need to pee like a race horse. It was only afterwards, after the need to focus and the adrenaline subsides. I've heard the same thing from military personnel, contractors, and LEOs while engaging in focused shooting.

Yeah, it's nicer to use a rifle that doesn't blow back my face. But there are a whole lot bigger issues -- applying the fundamentals, focusing on the targets & surrounding environment, attention to safety. Gas is a nothing burger IMO.

Wow! I would think that much pressure held by the gas port would cause it to wear significantly prematurely if used on "no gas" frequently.

quote:

Originally posted by hrcjon:
this is not an actual contribution to the discussion, but simply an odd observation. I have a CZ Bren 2 that the gas piston allows a position of 'no gas'. What amazes me when I shoot it that way is that when you pull the bolt back there is literally no gas vented. like none. I fully get the the valve selection has shut off dumping it back into the receiver via the gas port, but I would have expected some residual in the barrel that would vent to the ejection port when you cycle the weapon.

I have no idea if what you suggest actually happens and there is port wear in excess of the normal amount when venting. But it matters not. The gas flow is ultimately regulated by the size of the orifice in the piston, not like in an AR where what matters is the size of the gas port. For sure the piston can wear, but its an easily replaceable part. And in closed gas position all you would expect is erosion at some level on the surface so not a big issue.

quote:

Originally posted by fritz:
Yeah, it's nicer to use a rifle that doesn't blow back my face. But there are a whole lot bigger issues -- applying the fundamentals, focusing on the targets & surrounding environment, attention to safety. Gas is a nothing burger IMO.

It doesn't sound like your gas to the face experience with your LWRC was that bad then. I've had gas to my face that felt like getting slapped with a handful of needles, every shot. It HURT, and wasn't even with a rifle. On another weapon I've had my eye nearest the ejection port water so bad with the ammonia vapor that I couldn't see out of it for a minute or so. That was when tilting it to use an offset micro red dot for close quarters shots.

The point is, YMMW with gasiness.