Shorter Barrel with a Silencer

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  • thperez1972

    ESSAYONS
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    I've run out of AR build ideas. With a couple of suppressors on the way, I have a couple of new ideas but, being new to the world of suppressors, I wanted to get some input first. I'm toying with the idea of a really small barrel for a range gun. I'm not planning to set any distance accuracy records, just something to play with in the 25-50 yard range. The Sandman S has no barrel length restriction so, theoretically, I should be able to suppress a 2" barrel but I don't believe I will do that. My initial thoughts would be a 7.5" barrel with a 12" handguard and a muzzle brake to act as a sacrificial blast chamber. That would give an overall "barrel length" of just over 14". With an SBA3 pistol brace, I don't think this would be too uncomfortable to shoot. It may feel like picking up my old issue M4. Because this would be a "play gun," I'd likely stick to 223 for the cheaper ammo but I haven't completely ruled out 300 blackout. How bad would this be on the pistol length gas system and the BCG? Is there any reason this would simply be a bad idea?
     

    jcomar1

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    With a 7.5" barrel 556 suppressed under the handguard, the handguard will get so hot so quick you won't be able to shoot it for long.
    I have a 10.5" barrel with a 12" handguard and tucked can, and the can is only tucked about 3"... but it gets super hot quick. Point is, if you go short don't tuck the can, or don't plan on being able to do mag dumps or shoot it for long periods of time. Also if it's not a direct thread then it will be hard to release the QD system under a handguard. I tried it once and it was too much of a pain.
     

    thperez1972

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    You may want to consider an adjustable gas block.

    Good idea.

    With a 7.5" barrel 556 suppressed under the handguard, the handguard will get so hot so quick you won't be able to shoot it for long.
    I have a 10.5" barrel with a 12" handguard and tucked can, and the can is only tucked about 3"... but it gets super hot quick. Point is, if you go short don't tuck the can, or don't plan on being able to do mag dumps or shoot it for long periods of time. Also if it's not a direct thread then it will be hard to release the QD system under a handguard. I tried it once and it was too much of a pain.

    One is a dead air. It's not direct thread but there's release. The other is a silencerco but the silencerco attachment point will be replaced with one from dead air made for the silencerco. But the heat is something to certainly consider. Maybe I should consider the 9" handguard to reduce some of the heat.
     

    John_

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    I'm sure you realize a super short barrel on a 5.56 AR is counter productive to a silencer to begin with. 5.56 was designed for a 20" barrel from the beginning. When you go down to less than 10", the velocity losses are huge, and massive muzzle flashes become apparent. (powder burn outside of the barrel) One of the reasons .300 AAC has a big edge to 5.56 in SBR or pistol length barrels, btw.

    So why do you want to build a 7.5" barrel 5.56mm and put a suppressor on it? I sure hope you don't plan on full auto with such a short barrel and silencer. I'd do a .300 AAC SBR before a 5.56.
     

    thperez1972

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    I'm sure you realize a super short barrel on a 5.56 AR is counter productive to a silencer to begin with. 5.56 was designed for a 20" barrel from the beginning. When you go down to less than 10", the velocity losses are huge, and massive muzzle flashes become apparent. (powder burn outside of the barrel) One of the reasons .300 AAC has a big edge to 5.56 in SBR or pistol length barrels, btw.

    So why do you want to build a 7.5" barrel 5.56mm and put a suppressor on it? I sure hope you don't plan on full auto with such a short barrel and silencer. I'd do a .300 AAC SBR before a 5.56.

    https://www.bayoushooter.com/forums...h-a-Silencer&p=1630715&viewfull=1#post1630715
     

    John_

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    This is a great article written (2012) on barrel length and the 5.56x45mm cartridge. In this study, they cut an inch off at a time, and recorded the results/data. A great reference for AR lovers.

    http://www.sadefensejournal.com/wp/?p=1093

    When you get down to 10" barrel lengths or less, you compromise the very strength of the 5.56 cartridge, high velocity and projectile fragmentation. At least for a human killing tool.
     

    oppsImissed

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    I did a 14 inch a while back with a can. It was a nightmare.
    Wouldn't cycle. I changed barrels and gas systems. Tried adjustable gas blocks. You name it. Finally got it to run subsonic after I drilled out the gas block.
    Good luck.
     

    thperez1972

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    This is a great article written (2012) on barrel length and the 5.56x45mm cartridge. In this study, they cut an inch off at a time, and recorded the results/data. A great reference for AR lovers.

    http://www.sadefensejournal.com/wp/?p=1093

    When you get down to 10" barrel lengths or less, you compromise the very strength of the 5.56 cartridge, high velocity and projectile fragmentation. At least for a human killing tool.

    I read various studies regarding barrel length on an AR and I understand all this but it is not relevant to the question I'm asking. I'm not asking if it would an efficient setup. It's not. I'm not asking if there are better configurations. There are. As stated, and obviously overlooked, in the original post, this would be a range gun. I'm asking if there's any reason that specific configuration, in and of itself, is a bad idea.
     

    thperez1972

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    I did a 14 inch a while back with a can. It was a nightmare.
    Wouldn't cycle. I changed barrels and gas systems. Tried adjustable gas blocks. You name it. Finally got it to run subsonic after I drilled out the gas block.
    Good luck.

    I have a 16" 556 (AR platform), a 9.5" 300 (AR platform), and an 18" 308 (HK91 platform) they will mainly be used on. I also have a 10.5" 556 I use for critter control on our 20 acres. I'm going to try it on the 10.5 as well. If it doesn't work on that one, I may try an adjustable BCG. It's got a front sight post so an adjustable gas block isn't a real option. I have enough "working" guns to use them on. But I'm trying to stay away from subsonic 223 rounds. If it comes to that being the only option, the gun won't be a viable host, in my opinion. I'm hoping the can comes in soon and I haven't even started on the "stupid" build yet so I'll likely wait and see if the can works on the 10.5 first. But your experience doesn't inspire confidence in my range gun build idea.
     

    oppsImissed

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    I have a 16" 556 (AR platform), a 9.5" 300 (AR platform), and an 18" 308 (HK91 platform) they will mainly be used on. I also have a 10.5" 556 I use for critter control on our 20 acres. I'm going to try it on the 10.5 as well. If it doesn't work on that one, I may try an adjustable BCG. It's got a front sight post so an adjustable gas block isn't a real option. I have enough "working" guns to use them on. But I'm trying to stay away from subsonic 223 rounds. If it comes to that being the only option, the gun won't be a viable host, in my opinion. I'm hoping the can comes in soon and I haven't even started on the "stupid" build yet so I'll likely wait and see if the can works on the 10.5 first. But your experience doesn't inspire confidence in my range gun build idea.

    Like I said. To get it to run a true, quiet, subsonic round was a nightmare. But It did make regular 556 rounds a little more tolerable without ears on. It was one of those things where I was told I couldn't do it. Well, next time I'll listen. But on the plus side, I built 3 more uppers with all the left over barrels
     

    AK shooter

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    I'm going to watch this later but I read his first comment and he got it working. I'll try to see if he used any adjustable stuff or just happened to come across a working configuration. Thanks.

    I didnt watch it all either. Like most of these videos there us too much talking and less product usage.
     

    Jmfox3

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    I've done a 300 BLKO, 12 in barrel, suppressed, gas piston, adjustable gas block, intended for subsonic rounds. Everyone else has commented on the 5.56 problems for subsonic. A subsonic build, even for 300 BLKO, is not a trivial undertaking. You'll need to play with piston springs, buffer springs, buffer weights, magazines, bullet weights, and powder charges to get the gun cycling correctly. If you're not patient I don't recommend it.
    All said, I found the build itself to be very rewarding and learned even more about the AR in the process.
    Good luck.
     

    rcm192

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    I've done a 300 BLKO, 12 in barrel, suppressed, gas piston, adjustable gas block, intended for subsonic rounds. Everyone else has commented on the 5.56 problems for subsonic. A subsonic build, even for 300 BLKO, is not a trivial undertaking. You'll need to play with piston springs, buffer springs, buffer weights, magazines, bullet weights, and powder charges to get the gun cycling correctly. If you're not patient I don't recommend it.
    All said, I found the build itself to be very rewarding and learned even more about the AR in the process.
    Good luck.

    Thats half the fun! Try adding a pdw stock with a mini style buffer and flat spring into the mix. Thats when **** gets interesting with a 7.5" barrel. Although I dont run that one suppressed, I do have a 9" blackout DI upper that has no issues with my omega 30 supers or subs.
     

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