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How do Silencers Impact Blowback?

When you first start learning about silencers, one of the terms you’ll start seeing tossed around is ‘blowback’.

In this article we’re going to explain:

  1. What blowback is
  2. How different weapons are impacted
  3. How to prevent it from causing problems

Keep in mind that many modern suppressors are specifically designed to reduce blowback; so, if you’re worried about it give us a call and we’ll help you select a model that will fit your needs.

What is Blowback?

In order to illustrate the concept, let’s look at an extremely common semi-automatic weapon: the AR15.

When you pull the trigger on your AR15, you’ll set in motion a series of events – which can be simplified into these steps:

  1. The powder is ignited – which creates the pressure required to send the bullet down the barrel (with gas expanding behind it)
  2. Once the bullet passes the gas block (which is typically under the front sight post or rail), some of the gas is redirected back through the gas tube and into the chamber
  3. The gas pressure entering the chamber allows the bolt to unlock and cycle – which loads the next round into the chamber

 

The gas that goes back into the chamber is called ‘blowback'; and, hopefully it’s clear that blowback is required to make your AR15 operate correctly.

What is Blowback?

Keep in mind that, although many people tend to focus on the gas coming back through the gas tube – a lot of gas also comes back through the barrel itself after the bolt is unlocked.

In this example, imagine adding 6″ of additional barrel length without moving the gas port – and you’ll start to get an idea of how blowback can be bad.

As the barrel length is increased, so is the amount of pressure sent back through the gas port & barrel.  This increased gas pressure will cause the bolt to unlock a bit earlier and cycle faster.  It will also force more gas into the chamber as the weapon is cycling.

Now, just start thinking of your suppressor as a barrel extension (which is exactly why you’ll get a velocity boost when using a silencer).  Do you see why blowback comes up so often when talking about silencers?

How are different weapons impacted?

At this point, let’s move away from the AR15 example and start focusing on different styles of weapons:

Single Shot Weapons (such as bolt action, lever action, break open, etc…)

Weapons that are cycled manually aren’t impacted by blowback at all.  In those cases, adding a suppressor won’t have any negative effects – and you’ll benefit from reduced sound, increased accuracy & range, and reduced recoil.

Gas Blowback Weapons

The AR15 we already talked about is a common example of a gas blowback weapon – but there are many others.

In this case, the additional blowback can cause several issues:

  • The faster bolt speed will cause the carrier & bolt parts to wear out faster – although this typically isn’t noticeable for most users.
  • Since the bolt is cycling faster, it’s possible to actually outrun the spring in your magazine.  (This is often referred to as Bolt-Over-Base.)  In this case, your weapon will either jam or lock up on an empty chamber.
  • The weapon will get dirtier faster since there is more gas in the chamber.
  • You’ll generally smell more gas; and, depending on the weapon, may feel it blowing into your face & eyes as you shoot.

Fortunately, there are several easy ways to get the blowback levels back to optimal levels.

Recoil or Piston-Based Weapons

There is a lot of confusion about using a suppressor with piston weapons.  The biggest source is when people assume all the blowback is coming through the gas tube of gas blowback weapons.

As we already mentioned, a portion of the blowback also comes through the barrel itself; so, most of the same problems that occur with Gas Blowback designs will also happen with piston & recoil designs.

How can you prevent too much Blowback?

Although we’re going to focus on the AR15/10 style weapons here – these same concepts will apply to pretty much any gas-operated firearm.

Before going any further, if you’re not having negative issues – don’t try to solve a problem that doesn’t exist.  If you’re having one or more of the issues described above, try these simple suggestions:

  • Use a heavier buffer – This will slow your bolt back down and will solve most cycling problems for just a couple of bucks
  • Try a Gas Buster or Griffin SN-ACH charging handle – If you want to reduce the amount of gas escaping around the charging handle, then this is a great accessory!

GemTech Suppressed Bolt CarrierIf you want the ultimate solution, then I’d recommend the Gemtech Suppressed Bolt Carrier (also availabe for an AR10).  These bolt carriers work wonders and are adjustable so your weapon will run optimally in either suppressed or unsuppressed mode.

(But… Why would you run unsuppressed?)

For Piston-Based Weapons, most modern designs include some type of suppressed adjustment.  This adjustment is there specifically to tune the weapon when running a suppressor – and it’s easy to use in most cases.

For Recoil-Driven Weapons, you generally won’t have any serious problems; but, if you do try using a slightly heavier recoil recoil spring.

Conclusion

At the end of the day, blowback isn’t a huge issue on most weapons.  If you do run into it, try going through some of the solutions listed here – or give us a call and we’re happy to help.

21 Responses to “How do Silencers Impact Blowback?”

  1. Chris says:

    You have a “grammatical error” or “spelling error” depending on who you ask. In this paragraph:

    Gas Blowback Weapons

    The AR15 we already talked about is a common example of a gas blowback weapon – but there are many others.

    In this case, the additional blowback can cause several issues:

    The faster bolt speed will cause the carrier & bolt parts to wear out faster – although this typically isn’t noticeable for most users.
    Since the bolt is cycling faster, it’s possible to actually outrun the spring in your magazine. (This is often referred to as Bolt-Over-Base.) In this case, you’re weapon will either jam or lock up on an empty chamber.

    The last sentence is where the error occurs. The word “you’re” SHOULD be “your”. “you’re” is a contraction of two words “you” and “are”, which would just sound wrong if you said it using those words. “your” is referring to my possession, which is what the article is referring to.

    And that’s my 2 cents on the subject.

  2. Rob says:

    Are there any solutions/techniques available to reduce the amount of fouling/extra carbon that ends up getting pushed into the chamber, BCG and receivers? I’m not concerned with gas in the face because I have a PRI on each gun I run suppressed, they work pretty well, and the bolt speed issue is already dealt with as well through various means whether through adjustment of the gas system through a Noveske gas block or Sig/Swiss Arms or Scar, etc. or through additional bolt weight if on a lesser system. But as you pointed out, none of those address the real, big, problem and that is the massive build up of crap in the chamber and receivers. Not only does it severely impact how long you can go before being forced to clean, it dirties up your cases, it makes cleaning take a good 3x longer than normal and it makes a total mess.
    Is the solution to vent more of those gases out somewhere so they don’t backstop in the receiver/chamber? Hopefully some research is being done in this area as we become more prolific with cans. I love my cans, and I try to use them all the time, but this is the big hold up for me currently because each time I use them I can count on having to spend a lot more time after the fact dealing with the mess they’ve made. Even my reloading efforts are hampered because I now have cases which are so dirty I can’t even read the headstamp on them.

    • bill says:

      Same comment/question as Rob. My suppressed 10/22 gets filthy f-a-s-t! Wouldn’t fire after maybe 100 – 150 rounds because there was too much fouling on the bolt face. I’m not shooting cheap ammo but I’m not shooting Gemtech’s either. Finding it in stock has been challenging.

  3. NVStorm says:

    Nicely explained, clearly written. I don’t really have a serious need for a suppressor but apparently it’s pretty simple to get the sign off where I live. I must convince the finance minister that it will make our neighbors happier.

  4. Chucky says:

    Just a comment on the term “Blowback”.
    Blowback is term used in firearm design to describe simple action that does not have any locking mechanism and barrel remain stationary. On many .22 caliber handguns and rifles, and some 9mm submachine gun the operation of action is blowback type operation. Even though there isn’t any gas blowing back at the slide or action.
    I don’t what the right term is for this problem certain blowback is intuitive but it also been used to describe something else.

    • jeremy@silencershop.com says:

      You are correct. In talking about the excess gas caused by adding a silencer it is often referred to as “blowback” since most people are familiar with that term.

  5. Pat says:

    On an AR-15 platform for a given barrel length (say 16 or 18 inch), which is more susceptible to blowback, a mid-length or a rifle-length system?

  6. Mark says:

    Still new to cans. Was shooting last weekend with a few diff platforms. I built a 10.5″ 5.56 Adams Arms piston upper, ran flawless with YHM Phantom. Almost no blowback. Friend shot 10.5″ 5.56 with Gemteck Suppressed BCG, a little more blowback but still ok. Then a 16″ 5.56 with no mods……pretty bad. However, I then shot my G17 with Gemteck 9 and G21 with Tyrant 45. BOTH guns was literally throwing crap in my face with Federal HST….it was very irritating. But when I switched to vanilla FMJ for the 45 and subsonic FMJ for the 9, no more debris in my face. Why am I getting debris in my face shooting quality defense ammo? Also, not to sound like an idiot, but can someone explain the difference between blowblack, delayed blowback, browning tilt/lock etc. Like I know my AR is diff form my 92FS which is diff from my Glocks with is diff from my SR-22….etc….thanks…..good article btw..

    • jeremy@silencershop.com says:

      This is common with the AR platform. I would suggest looking at charging handles like the Griffin Armament SNACH charging handle. It will help vent the gas away from you. Also if you add the GEMTECH bolt on the suppressed setting then it will help even more.

  7. Charlie Z says:

    Any suggestions on reducing blowback on a semi-automatic pistol like a Glock?

    • jeremy@silencershop.com says:

      Not really much you can do except change the ammo or silencer. A larger silencer on a small bore will have less blowback.

  8. Pat says:

    I have a Saker on an 18″ midlength.

  9. Adam says:

    I’ve been looking at pistol caliber carbines (all seem to be blowback operated). Which do you think are the best platforms for suppression (specifically which will give the least gas in the face?)?

    Thanks!

    • jeremy@silencershop.com says:

      All pistol caliber carbines seem to do well with blowback. There isn’t as much gas as an AR shooting 556.

  10. Adam says:

    I have an interesting problem that I am hoping to find a solid answer for.

    I currently have a 300 AAC SBR, running a pistol length upper (10.5 inch with a standard pistol length gas tube and non adjustable gas block)

    The buffer and spring are also pistol variants.

    It shoots and cycles subsonic 220gr SMK all day, suppressed and un-suppressed. In fact, I have never had a FTF or FTE with it. I am happy about that.

    The reason I built this rifle is to hunt feral hogs, preferrably at night, with or without a suppressor. Being able to use subsonic ammo is great, but supersonic ammo is required to effectively dispatch a hog at a distance.

    The problem I have is that the rifle cycles supersonic 175g 300 AAC ammo reliably, but it hits hard. The recoil is very hard when fired. I am not complaining about recoil, I am worried about overgassing my rifle and breaking something. It cycles so hard, I do not think that attaching my suppressor to it would be a good idea.

    I know suppressors do not “silence” supersonic rounds, but they do make them hearing safe. I think that if I put the can on my rifle and fire a 175g supersonic round through it, it will easily over-gas my rifle.

    The whole point of having the 300 AAC is so that I can shoot supersonic and subsonic ammo through it. My suppressor (Silencerco Harvester 30) can handle up to 300 Win Mag. I would like to be able to shoot subsonic when I like, and also shoot supersonic with the can without breaking my rifle.

    What options do I have? I looked into adjustable gas blocks, the WAR upper, and the Gemtech bolt carrier.

    I simply need something that can handle the supersonic ammo and still be able to shoot subsonic.

    • jeremy@silencershop.com says:

      You listed all the fixes for your gun. The adjustable gas block, WAR upper, Gemtech bolt, and a heavier buffer/spring. Adjustable gas block would be the best place to start and then the buffer. Since the gas block will reduce the amount of gas going in the receiver. Also look at where you brass is ejecting. You want it going in the 3-4:30 position. If it is forward then it is overgassed. Past that and it is undergassed.

  11. joe koehler says:

    I have personally tried everything for gas blowback. I have tried the heavier buffer spring, the gemtech bolt carrier and the gas block buster. Nothing seems to work, i have a daniel defense v3 with a sure fire soccom suppressor. The blowback is so bad my eyes water after 5 rounds. I have talked to some former seals at my shooting range and they said unfortunately its just the nature of the beast. There is not a whole lot you can do about it but just deal with it. I think its just a matter of time until someone gets the technology right and fixes this issue.

    • jeremy@silencershop.com says:

      That is very odd that nothing fixed it. Especially since you were using a Surefire which is over bored so there is less blowback.

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