Suppressed rifles get very dirty

800px-patent-de1553874-07-oct-1971-handfeuerwaffe-mit-schalldaempfer-heckler-und-koch-1-tm.jpg

The fact that guns get dirty is is one of those unfortunate facts of life, along with death and taxes.

A piston operated gun will reduce the dirt that enters the rifle compared to a direct gas impingement gun (AR-15). When you add a suppressor, I think it makes little difference what type of gas system your rifle uses, it is going to get very dirty!

800Px-Patent De1553874 07-Oct-1971 Handfeuerwaffe Mit Schalldaempfer Heckler Und Koch-1
From the patent of an early model MP5SD suppressor.

A suppressor works by slowing down the gas through a series of baffles. The slower moving gas makes less noise as it is vented out of the can (can = slang for suppressor). The downside is that on a autoloading firearm once the action cycles and the spent cartridge is ejected there is more pressurize gas in the system than there would be without a suppressor. This gas, along with carbon, dirt, unburned power, is vented into the rifle action. Without a suppressor this still happens but the pressure inside the barrel is lower because the gas is vented faster.

“new-arguy” posted photos at AR15.com of his HK 416 upper (piston AR-15 upper), which had a AAC 416 suppressor attached, after firing 2000 rounds without cleaning.

This is my HK 416 upper, I ran it with an AAC 416 silencer at the last Magpul Dynamics class here in St Augustine. 2 days, 2000 rounds. I only took the silencer off the start of day 2 for a few drills, I would guess about 150 rounds. All the rest were with the can. I dropped some lube in the gun at the start of the class, aside from that, no cleaning, no oil, nothing at all. No problems either, well, not really. I will admit, I have run regular DI guns like this without problems, but I needed to keep dumping oil on the bolt group. In fact, one of the guys who works with me ran his Noveske N4 with a AAC M4 2000 right next to me the whole class. His gun ran fine as well, but he did keep dumping lube into the bolt carrier.

Anyway, the gun was fiilthy. I have never cleaned a gun that was so dirty. Grime and crud was seeping out between the upper and lower trying to escape. It is worth mention that a large piece of carbon built up and fell under my trigger group toward the end of the second night. I thought it was a primer, but when I opened the gun up and shoot the lower, it was plainly a piece of carbon. So technically, the gun did comletely fail. I have seen this same thing happen one other time, in another Magpul class (actually the one from the last DVD). My friend Derek was running a gun with a can on it for about as many rounds. Same thing, crud kept building up until some of it found its way under the trigger group.

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bigbore, of adcofirearms.com, posted photos of his AK-74 rifle after firing 2000 rounds of corrosive ammunition using a suppressor and leaving it sit for a week.

Ak-74 4

Ak-74 3

After leaving it sit for a week, the bolt rusted into place and it was no more than a club.

A problem with some of the now discontinued Ruger Police Carbine and Marlin Deer Camp, blowback autoloader pistol caliber carbines, was that their actions got very dirty. A pistol in the same caliber with a 4″ barrel would vent gas much faster than a 16.5″ barreled carbine.

300Px-Ruger Pc4
Ruger PC4 (Police Carbine .40 S&W).

There is no substitute for cleaning your rifle. If you are considering a suppressor this is something to take into account. Bolt/lever/single shot action rifle with suppressors will not have this problem. The gas will be vented before the action is manually cycled. I personally have not had any problems with .22 semi-autos rifles with suppressors, nor have I heard of anyone having problems.

Many thanks to Jay for emailing me the link to the photos.



Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


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  • Matt Groom

    If you use a can, you must clean your gun immediately after firing, the same as if you were shooting black powder and corrosive primers. Whenever I have to clean a gun that’s been shot with a can on it, I generally soak all of the metal components in Mineral Spirits for an hour or so, which causes most of the sticky fouling wash off. Mineral Spirits is cheap to buy by the gallon, so you can generally soak the whole gun with no problem. Its free of Ammonia, won’t harm anodizing (unlike Hoppes No. 9), and it won’t melt most plastics. Actual carbon build up usually requires more intense cleaning, and Copper fouling requires Copper Cleaner to remove. Your mileage may vary.

    The folks at AAC tell me that the best lubricant to use with a dirty, suppressed firearm, such as anything full auto, is Synthetic, 2-cycle motor oil, but I haven’t tried it yet.

  • Mike

    I’m a bit of a newbie, so excuse the lack of knowledge, but what is the difference between a gas blowback and piston operated rifle?

    • Mike, blowback uses the force of the gas in the barrel to push open the bolt and cycle the action. A gas operated firearm siphons off gas at some point along the barrel, the gas then travels along a gas tube and either pushes against the bolt carrier (the thing that moves the bolt) directly (eg. AR-15), or pushes a piston which pushes against the bolt barrier (eg. AK-47, M1 Garand, M14).

  • Mike

    Thanks Steve

  • jdun1911

    AR15 DI is considered a gas gun. However it does have a piston. It’s part of the bolt.

    Click on the glass to see how an AR15 DI works.
    http://www.bushmaster.com/anatomy_bushmaster.asp

    Piston rifle.
    http://www.youtube.com/watch?v=WvX6sXs_ZO4

    I find it silly that people keep saying that piston guns run cleaner then gas gun. They actually believe that the carbon magically disappear in a piston firearm. It doesn’t, the filth is deposit in a different place.

  • jdun1911

    I am surprised that the HK416 piston didn’t bind to the tube. With that much filth and a small tube you would think it would. Then again carbon is a lubricant until it becomes solid.

  • Puke

    Taxes are not a fact of life!
    Dammit I hate that retarded saying.

    Theft is never acceptable.

    • Puke, fair enough, I don’t disagree with your statement. A fact of my life then 😉

  • Nick

    “The downside is that on a autoloading firearm once the action cycles and the spent cartridge is ejected there is more pressurize gas in the system than there would be without a suppressor. ”

    Not all firearms. I know of the Swiss SG 550 series of rifles has a value to allow only the needed amount of gas through. I wonder if these will run as dirty?

    “Once inside the gas cylinder, propellant gases pass through an L-shaped channel machined in the piston head and are directed forward towards the gas valve. The pressure build-up in front of the piston head pushes the piston and bolt carrier rearward. As the piston is driven back, the gas port and the L-shaped channel move out of alignment, cutting off the supply of gas to the cylinder. Surplus gas and powder residues are evacuated through an exhaust port in the gas cylinder. This system ensures that only the precise volume of gas required to overcome the mass and resistance of the rifle’s moving assembly is admitted from the barrel.”

    • Nick, based on your comment (not on any experience), it sounds like the system is designed to prevent excess force being applied on the piston (and therefor the bolt carrier), and would not effect the backpressure in the barrel.

      Anyone else what to chime in?

  • Matt Groom

    Firearms are mechanisms which utilize chemistry to create an artificially high atmosphere in a controlled environment in order to push a projectile in a predetermined direction. The problem is the sudden release of that pressure into the ambient environment.

    Based on my somewhat limited understanding of fluid dynamics, the pressure and gases which cause fouling will continue out of any available opening, following the path of least resistance.

    There is no system which can operate the action based on the higher pressures within a firearm that will be able to utilize all available gasses without any waste, and no system of vents, valves, or pressure releving cells that could change the higher than atmospheric pressure inside of the bore to the ambient atmospheric level before that action was able to cycle.

    When the action cycles, it breaks the seal created by the fired cartridge case. The barometric pressure inside of the receiver and action behind the breech will be equal to that of ambient barometric pressure of the surrounding environment, and when that seal is broken, those gases will travel backwards into the action at the same rate they will escape any other place in the system. You could probably calculate the pressure of the gases which escape into the action and pressurize the inside of the action with Nitrogen or some other inert gas to counter that back pressure, but that would be very impractical, even in suppressed machine guns.

    By the time the action has moved any significant amount, the bullet has exited the barrel, and the gas pressure has already begun to vent out of the muzzle. The shorter the barrel, the less time this takes. But when a suppressor is used, the entire purpose of is to act as a hindrance to the natural flow of the gases, to slow them down and turn the movement of gaseous particles, which is observed in the environment as sound, and turn it into heat, by forcing those gases through a series of baffles. A suppressor could theoretically be too efficient, and block so much gas that would otherwise escape out the muzzle that when the action opened the effect would be the same as when an over-pressure round causes a case head separation. Boom!

    Suppressors slow the release of gases. If the weapon uses those same gases to operate its action, then some of those gases will escape into the action. There is no way to capture that energy and utilize it after that energy has been transformed into heat or escaped into the atmosphere without the use of electronically controlled motors and power cells. There will be blowback, and suppressors will make that blowback worse.

  • Wow that photo of corrosive ammo and then letting it sit is just nasty. I can imagine letting my Daniel Defense M4 get that bad.

  • That AK-74 pic is just WRONG!

    My arse would be twitching putting it away overnight without a cleaning, expecting a sergeant’s boot to connect at any time!

  • […] Suppressor fouling […]

  • bob r

    Matt Groom:
    “There is no system which can operate the action based on the higher pressures within a firearm that will be able to utilize all available gasses without any waste, and no system of vents, valves, or pressure releving cells that could change the higher than atmospheric pressure inside of the bore to the ambient atmospheric level before that action was able to cycle.

    There is no way to capture that energy and utilize it after that energy has been transformed into heat or escaped into the atmosphere without the use of electronically controlled motors and power cells. There will be blowback, and suppressors will make that blowback worse.”

    I suspect this is not correct; maybe not easy to do but not necessarily impossible.
    One possibility:
    A spring is positioned between the gas piston and the bolt, latches are placed on both sides of the spring.
    The latch on the action side of the spring is connected to barrel and high pressure gas will prevent the spring from moving; release of the latch will allow the spring to move toward the bolt.
    When the rifle is fired, the gas piston will compress the spring; the second latch will engage automatically as the spring is compressed. The purpose of the second latch is to prevent the spring from moving toward the piston when the gas pressure is lowered. The second latch is released by the bolt moving forward.
    Sequence:
    1. Ignition
    2. Bullet passes first latch port and latch stops spring movement toward bolt.
    3. Bullet passes piston port and piston compresses spring against first latch. The latch on the piston side prevents the spring from decompressing.
    4. Bullet leaves barrel.
    5. Pressure reduced to a level that allows first latch to release and spring pushes bolt to the rear.
    6. Bolt moves toward chamber which releases the latch on the piston side of the spring.
    7. Repeat as necessary.

  • Big Daddy

    Checkout this guys system. That looks like it solves all the problems of suppressed weapons.

  • Matt Groom

    Quite right, Bob R. I should have written “There is no practical way…”. I myself envisioned some kind of complex mechanical clockwork that would take the kinetic energy and transmit it through a series of springs and gears to operate the action. The timing of any system would have to be extremely precise, and even with a system like yours that is seemingly less complex than the mechanical system I envisioned, it would still be an unnecessary and impractical expense to temporarily avoid the inevitable.

    But you are correct in your assertion that it is not impossible. Nothing is impossible. I tend to speak in terms of absolutes as a habit from arguing political philosophy, which follows a different set of rules from the temporal realm, to be sure. There’s also the Gatling system, which conceivably does not pull the fired case from the chamber until the pressure has become ambient.

    I read once that David Marshal Williams of M1 Carbine fame once created a blow-forward operated rifle just because someone argued with him that it could not be done.

  • J Fulkerson

    For whatever it’s worth, I have an AAC Pilot Suppressor on the threaded 16 inch barrel of a Ruger 10/22. I love the can but it does make the Ruger action very dirty very quickly.

  • hrt4me

    Interesting discussion

  • DeadPatriot

    I’ve been experimenting with AR’s and my YHM suppressor for a couple of years. I’m a tinkering addict and hate dirty weapons, so the massive buildup was cause for an epic modification adventure.

    Going from direct impingement to piston DID help, but not in an extreme fashion. The grime went from solid to more slimy. It still took about 3-4 hours of cleaning to get it up to my standards (yes, I’m anal).

    After some mental gymnastics, I convinced myself that adding a silencer was basically like extending the barrel. You’re adding a section on the end that still contains pressurized gas. The obvious solution seemed to shorten the barrel. With my YHM quick detach muzzle brake, I was able to shorten my carbine-length by about two inches while still being legal with the brake welded on. The result? It also helped. A lot. It’s not back to where it was before the suppressor, but it’s tolerable.

    I’d really like to shorten the barrel more, but that’s another set of fingerprints, another $200, and another several months of waiting. Hope that info helps.