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Old October 11, 2017, 01:19 PM   #1
simonrichter
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What happens if an unmodified AR15 is fired with a can?

What exactly is supposed to happen when a direct gas impingement system is fired with a suppressor w/o modifications on the gas valve? Will the overpressure cause the system to kinda explode or will it just malfunction?
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Old October 11, 2017, 01:30 PM   #2
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I have done it many thousands of times and as far as I know, absolutely nothing happened other than the bullet going down range and the action cycling. And.........it wasn't as loud.

In fact, this is the first time I have ever heard that something MIGHT happen.
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Old October 11, 2017, 02:05 PM   #3
T. O'Heir
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A suppressor is nothing more than a muffler. Just like the one in your car. It doesn't fiddle with the gases at all. It fiddles with the sound created by them.
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Old October 11, 2017, 02:15 PM   #4
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I too have shot many hundreds, if not thousands of rounds through a suppressed AR15 with no ill effects. Both my suppressed AR's have carbine length gas systems.


BTW, there is no such thing as a gas valve on an AR.
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Old October 11, 2017, 02:28 PM   #5
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That's good to hear. I'm awaiting for my suppressor to come in and I'm trying to look into what "mods" I need to do to my AR (pistol length gas system). Adjustable gas block, heavier buffer, stronger buffer spring, etc. I'll just leave the gun alone and see what happens when the suppressor comes in.
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Old October 11, 2017, 02:50 PM   #6
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"gas valve" is the wrong term, but I reckon there is a gas block that in some assault rifle types can be adjusted to firing rifle grenades, using blanks and - or so it appears to me - also for the use of a suppressor. Might be that this is only the case for other systems like long / short stroke and not for the direct impingement?

Maybe THIS might clarify what I'm referring to with my question (Number 5, to be exact)
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Old October 11, 2017, 03:03 PM   #7
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Yes you can have an adjustable gas block. Most rifles don't come that way but you can put one on if there is some reason you need it. And you can use it to tune your rifle.

But if your rifle is running fine the way it is, there isn't much point in getting one.

I have never had an adjustable gas block. FWIW: I probably own a dozen AR15 uppers and have owned an AR15 since about 1982.
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How the farmers gave them ball for ball,
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Under the trees at the turn of the road,
And only pausing to fire and load.
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Old October 11, 2017, 03:05 PM   #8
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"BTW, there is no such thing as a gas valve on an AR."

Well, sort of. All of my hosts have adjustable gas blocks or adjustable piston systems.
I wouldn't say "there's no concern" when adding a suppressor to a DI gun but it's not likely to explode. There is a concern that increasing the back pressure can cause undue wear and tear on the components so many users swap in a heavier buffer or adjustable gas block(and some don't). If the residual barrel pressure is excessive, the bolt may not close properly and may even cycle a "double feed".
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Old October 11, 2017, 03:54 PM   #9
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Right Mobuck, if you add a suppressor to an AR15, you will increase the pressure in the gas system. Depending on how the gun is set up, whether is is a carbine, mid length, or rifle length system, spring weight, buffer weight, etc., the addition of the suppressor most definitely CAN introduce cycling problems due to over pressure. Your BCG will likely cycle much faster as a result (which brings up the additional wear and tear you mentioned). Adjustable gas blocks can help mitigate the issue considerably.

You may find that if you have brass ejecting at 3-4 o'clock before adding the suppressor, that it starts landing at 1-2 o'clock. On a calm day or indoor range, you will likely notice a puff of hot gasses into your face, coming out around the charging handle after you add a suppressor.

From Silencer Shop https://blog.silencershop.com/silenc...pact-blowback/

Quote:
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.
I know that with 6.5 Grendel and 6.8 SPC AR15s, the addition of a suppressor will foul the cartridges in your magazine as you fire with each shot. Cartridges will be sooted, may tarnish, and you may actually get a build-up of gunk on them. This is from personal experience. It happens to a much lesser extent with .223/5.56.

Also, you do not want to leave cartridges chambered in your AR15 overnight or for long periods of time after firing several rounds. The cases can tend to stick in the chamber and may or may not cycle properly as a result. Extracting them manually can be extremely difficult. If you are storing a loaded, suppressed AR15 for SD purposes, store one that is clean.

While it may be correct to say that it is just a muffler, mufflers on engines affect how engines run via back pressure. So back pressure is an issue not just with the AR15, but with engines as well. https://en.wikipedia.org/wiki/Back_pressure
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Old October 11, 2017, 06:09 PM   #10
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Quote:
Originally Posted by T. O'Heir
A suppressor is nothing more than a muffler. Just like the one in your car. It doesn't fiddle with the gases at all. It fiddles with the sound created by them.
This is the second time I've seen you post this, and it's the second time I've pointed out that it's wrong. Every rifle silencer on the market except those from OSS will increase the gas pressure. Usually the rifle will still run just fine without modification, but not always.
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Old October 11, 2017, 06:14 PM   #11
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Quote:
Originally Posted by T. O'Heir View Post
A suppressor is nothing more than a muffler. Just like the one in your car. It doesn't fiddle with the gases at all. It fiddles with the sound created by them.
Say whaaaaaat!
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Old October 12, 2017, 06:00 PM   #12
hdwhit
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Quote:
What exactly is supposed to happen when a direct gas impingement system is fired with a suppressor...
In general, nothing out of the ordinary.

Suppressors/silencers work by redirecting the propellant gasses leaving the muzzle through a series of chambers where it can expand slowly enough that it is no longer supersonic when it enters the atmosphere.
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Old October 12, 2017, 10:55 PM   #13
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Quote:
In general, nothing out of the ordinary.
You didn't follow the thread, did you?
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Old October 13, 2017, 05:48 AM   #14
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In my experience the only cartridge that doesn't "foul the ammo in the magazine" is the 300BO. Even my AA piston uppers do this but to a lesser extent. I expected the piston system to take care of this but evidently the back pressure in the barrel is sufficient to blow carbon back past the case as the bolt is opening. A heavier buffer might decrease this but it's only what I'd call cosmetic so I haven't tested this idea.
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Old October 13, 2017, 02:50 PM   #15
Bartholomew Roberts
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Quote:
In my experience the only cartridge that doesn't "foul the ammo in the magazine" is the 300BO.
The top of all my .300 BLK PMAGs are all black, though the subsonic mags aren't as bad as the supersonics - I'd guess less gas volume is the reason.
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Old October 13, 2017, 04:33 PM   #16
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^^^ THIS^^^
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Old October 14, 2017, 06:48 AM   #17
highpower3006
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Quote:
"BTW, there is no such thing as a gas valve on an AR."

Well, sort of. All of my hosts have adjustable gas blocks or adjustable piston systems.
Sigh... I knew that there would be a nit picker out there.

Perhaps I should have been more pedantic and said that nearly all standard AR15's come with a fixed gas block, i.e. either a standard triangle front sight or a low profile gas block and only modified, rifles either factory or owner modified, will have adjustable gas port regulation.

While I know that there is likely to be some difference in port pressure between suppressed and non suppressed gas operated firearms, in the two examples I am familiar with, I can't feel any noticeable difference in felt recoil.

One is a standard 14.5" barreled M4gery with a AAC M4-2000 and the other is a SBR with a 10.5" barrel, running the same M4-2000. Both have standard carbine length gas systems and both cycle perfectly w/o the can. I expected the recoil to increase enough to notice when the suppressor in on the M4gery and was surprised that it felt the same.

On the SBR, I was concerned that I would have some cycling issues due to the extremely short dwell time after the gas port, but it seems to work okay unsuppressed and, like the other rifle, I can't notice any difference in felt recoil with the can on it. I have seen no evidence of increased wear on the bolt components but then I only have a few thousand rounds through it.

I do replace the gas rings from time to time, but I consider that to be a part of the normal maintenance on a gas operated AR.
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Old October 14, 2017, 07:50 AM   #18
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A friend of mine has a 10.5" SBR that he runs with a AAC M42K. When he first got the suppressor, the increased back pressure caused the gun to jam (bolt over ride) on just about every shot. A H3 buffer cured that problem. After that the only issue was the gas that blew out around the charging handle. A gasbuster handle with some gasket goo cured that problem.

In the case of my SCAR, I switch the gas block to the suppressed setting and have no problems other than the increased fowling in the receiver. I have not seen a suppressor that will not blow additional carbon into the chamber / receiver during extraction.
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Old October 14, 2017, 05:10 PM   #19
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I have an AAC M4-2000 and use it with a number of "stock" 16" and 10.5" DI guns, and havent seen any issues with reliability or function with any of them.

All of them will gas you at the charging handle, especially if youre shooting quickly, but a little Permatex solved that for the most part.

The only other thing Ive noticed is, with the suppressor on, ejection is more forward. With it off, more rearward.

I do get a POA/POI shift with a couple of guns, but not all of them.
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Old October 15, 2017, 01:41 PM   #20
Bartholomew Roberts
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The AR15 bleeds off excess gas through the two holes in the bolt carrier group as the gas pushes the bolt/gas rings back in the carrier. So it can already adjust itself some for excess gas pressure. However, where the gas port has been opened up to compensate for a short dwell time (10" barrels, 16" with rifle gas), adding a suppressor can cause a problem. LMT even makes a three-hole bolt carrier to address that.
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