Suppressed AR-308

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  • AmericanBob

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    May 10, 2009
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    Just took my first shots out of my 308 AR. This is my first venture into the large framed AR platform so excuse the inexperience. This is a factory Aero upper and lower, Aero 16 inch barrel, mid length gas system, standard Aero gas block, Magpul UBR stock so tube length is 7.75", KAK bcg, and Armaspec silent captured spring buffer. The barrel I had cut to 14" and had my suppressor mount pinned and welded on. Trying to make it slightly more compact for chasing pigs in the swamps of southern Georgia.
    Now that that is out of the way, the rifle is hoot to shoot. Unsuppressed it runs like a dream, an amazingly loud and flashy dream. Suppressed started out ok, but after about 15 rounds it started skipping over the top round in the magazine. It will lock back on an empty mag, but won't pick up the next round on a loaded mag.
    Any of you heavy shouldered shooters have any experience with this? Is it as simple as a heavy buffer and spring to slow the bolt down or do I need to look at something else? And yes, I should probably have had an adjustable gas block put on before the pin and weld, live and learn.
     

    88E30M50

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    Dec 29, 2008
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    Getting dirty and short stroking maybe? When I run my AR10 suppressed, I start having issues around round 20 too.

    Does suppressing an AR cause over or under gassing on an otherwise well set up rifle? I can’t remember but want to say under gassing.
     

    AmericanBob

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    Getting dirty and short stroking maybe? When I run my AR10 suppressed, I start having issues around round 20 too.

    Does suppressing an AR cause over or under gassing on an otherwise well set up rifle? I can’t remember but want to say under gassing.
    I don't think it's short stroking because it will run fine after I take the suppressor off and it will lock back on an empty mag with or without the suppressor.
     

    sloppyjoe

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    Mar 27, 2019
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    Getting dirty and short stroking maybe? When I run my AR10 suppressed, I start having issues around round 20 too.

    Does suppressing an AR cause over or under gassing on an otherwise well set up rifle? I can’t remember but want to say under gassing.
    Shooting with a silencer increases backpressure and causes overgassing - especially on AR10s. The extent of backpressure increase is largely dependent on the silencer design. Longer, tight bore silencers will typically have higher back pressure assuming a standard baffle stack.
     

    sloppyjoe

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    I would say yes, at least 95 percent of the time it will be suppressed. I'm running a YHM resonator.
    I havent tried it, but I've seen good reviews on gas limiting gas tubes. Since you cant remove the gas block, you could at least change the gas tube to a low flow one to help reduce your overgassing. You could also use a heavier buffer, but reducing the gas will probably have less felt recoil.
     

    AmericanBob

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    I havent tried it, but I've seen good reviews on gas limiting gas tubes. Since you cant remove the gas block, you could at least change the gas tube to a low flow one to help reduce your overgassing. You could also use a heavier buffer, but reducing the gas will probably have less felt recoil.
    Interesting, never heard of such a thing. Do you have a link?
     

    Slow Hand

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    Aug 27, 2008
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    I built an AR-10 a couple years ago using an Aero receiver set and hand guards, DPMS SASS barrel and other assorted parts. Rifle length on mine. Shooting unsuppressed it ran fine. Out the can on and it would often close the bolt on an empty chamber. Seemed under gassed which made zero sense. Shot some NATO spec 7.62x51 ammo through it and it ran fine. Realized teh NATO ammo was lower pressure and started trying things.
    I added an adjustable gas block, Tubb flat would buffer spring and still had issues. I finally machined a weight to fit in my BCG and changed from 168 SMK’s and varget to 150 SMK’s and 4895 and it runs fine now. I’m limited to 300 m, and the 150’s shoot fine out to that distance.

    Basically, with the higher pressure ammo and the can, it was over gassed and the bolt was outrunning the magazine. I had the heaviest buffer in it that I could find, so I couldn’t add weight that way. Like all things, it’s a balancing act. beef up the buffer spring and yes it opens slower, but the bolt also closes faster, so you haven’t gained much. Tubb used to make the BCG weights, but does not anymore. I found a picture and just took some measurements and made my own on the lathe. At the time, adjustable gas blocks for my barrel diameter were hard to find. If you’re using a standard diameter barrel, I bet you could find a two piece bolt together block and cut off yours and bolt it around your barrel vs. having to have your muzzle device un-pinned and re-pinned.
     

    sloppyjoe

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    Mar 27, 2019
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    I built an AR-10 a couple years ago using an Aero receiver set and hand guards, DPMS SASS barrel and other assorted parts. Rifle length on mine. Shooting unsuppressed it ran fine. Out the can on and it would often close the bolt on an empty chamber. Seemed under gassed which made zero sense. Shot some NATO spec 7.62x51 ammo through it and it ran fine. Realized teh NATO ammo was lower pressure and started trying things.
    I added an adjustable gas block, Tubb flat would buffer spring and still had issues. I finally machined a weight to fit in my BCG and changed from 168 SMK’s and varget to 150 SMK’s and 4895 and it runs fine now. I’m limited to 300 m, and the 150’s shoot fine out to that distance.

    Basically, with the higher pressure ammo and the can, it was over gassed and the bolt was outrunning the magazine. I had the heaviest buffer in it that I could find, so I couldn’t add weight that way. Like all things, it’s a balancing act. beef up the buffer spring and yes it opens slower, but the bolt also closes faster, so you haven’t gained much. Tubb used to make the BCG weights, but does not anymore. I found a picture and just took some measurements and made my own on the lathe. At the time, adjustable gas blocks for my barrel diameter were hard to find. If you’re using a standard diameter barrel, I bet you could find a two piece bolt together block and cut off yours and bolt it around your barrel vs. having to have your muzzle device un-pinned and re-pinned.
    Good call on the split gas block. I didnt know those existed. That definitely seems like the best solution here. Just dont damage the barrel when you take the death wheel to the current gas block.
     

    AllenM

    Diamond Collision Inc. Avon.
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    Apr 20, 2008
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    I have a CNMG and it was actually over gassed. I put an adjustable gas block on it and that solved my feeding issues
     

    T-DOGG

    I'm Spicy, deal with it.
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    248   1   0
    Feb 4, 2011
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    Another vote for the adjustable gas block. I played around with spring and buffer weight not too long ago with the 308 AR that I had. Looking back, it was mostly a waste of time and ammo.
     

    rb288

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    Apr 14, 2019
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    Well,it's probably to late now, but to run an ar 10 suppressed, you really need an adjustable gas block.
    When I made mine, I knew it was going to be run, primarily, suppressed so I put an adjustable gas block on it.
    It runs perfect and the only "issue" that comes up is if I decide to run unsurpassed, I need to readjust the gas. But not a big deal.
     

    Mustang1911

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    Oct 19, 2015
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    Are you running a carbine buffer and spring with the UBR stock? If so, might try an A5 buffer and spring system so you can get a heavier buffer than with a carbine buffer. Its only putting a band aid on the problem since 308 ARs are hard to suppress since they are ridiculously over gassed with a traditional suppressor.

    Best solutions are either a OSS/low backpressure can, or an adjustable gas block. Both would mean you'd have to take off your pinned muzzle device, but either of those would be the best solution - everything else is just an band aid without fixing the problem.
     

    AmericanBob

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    May 10, 2009
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    Are you running a carbine buffer and spring with the UBR stock? If so, might try an A5 buffer and spring system so you can get a heavier buffer than with a carbine buffer. Its only putting a band aid on the problem since 308 ARs are hard to suppress since they are ridiculously over gassed with a traditional suppressor.

    Best solutions are either a OSS/low backpressure can, or an adjustable gas block. Both would mean you'd have to take off your pinned muzzle device, but either of those would be the best solution - everything else is just an band aid without fixing the problem.
    Current buffer set up is an Armaspec silent capture buffer. I just ordered up a JP enterprises 2 piece adjustable gas block so I going to try that first.
     

    Angrysauce

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    Dec 30, 2020
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    I'd do one of the BRT gas tubes, just because I haven't ever used one and it seems cheaper than removing and reattaching a p/w.
    Heavier buffer may help, but it may also speed up the bolt going into battery. Trying one won't break the bank though.
    Get over powered magazine springs, +10% springs will speed up round presentation for loading.
     

    GSPBirdDog

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    Mar 21, 2010
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    How about a adjustable BCG? Though more expensive, I run one on my 6mm CM AR10 and it does amazing suppressed. I am also running a YHM R2 suppressor. I bought the Falkor Defense 308 BCG that comes with a set screw in the gas key. I am able to adjust it on the fly when doing load development by just popping the BCG out of the upper and tuning it whichever direction needed. I had to go with this BCG due to the Dracos barrel I am running has a proprietary gas block that's not adjustable.
     

    AmericanBob

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    So, I ended up ordering a BRT gas tube as well. I figured I'd try that first since changing the gas block is going to be a pita. And if this doesn't work, I still have the JP clamp on adjustable block I ordered. If it does work, great and then all I need is a creedmoor barrel and I'll have a second upper! I am amazed at the difference in gas port size. I'll report back after a trip to the range.

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