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Posted: 9/20/2009 10:56:33 PM EDT
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So I want to get a can for my Bushmaster M4. I was looking at the AAC M4. I read in the tacked thread about suppresors that I need to get my barrel rethreaded because Bushmaster may not have threaded the barrel perfectly concentric to the bore. How would you rethread it? Do they cut the end of the barrel off or what? Wouldnt that be illegal because the Bushmaster is already at legal length? Might be useful info for the tacked thread for us noobs who don't understand barrel rethreading. Thanks. |
| I have a stock bushmaster and Gemtech G-5. Haven't had any problems in over 10k rounds. When you put your can on run a cleaning rod or wooden dowel the size of the bore from chamber to muzzle. If you come out without issue and aren't scraping any baffles I'd go for it. Though having a professional gunsmith look at it isn't a bad idea. |
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So I don't need to get it rethreaded? I live in the boonies of Alaska and there are no gunsmiths around here that deal with Class 3. I am going to have to go to Anchorage to get it anyway. I just don't want to get baffle strikes in a 1k dollar suppresor. If anybody know exactly the process of rethreading could you explain it. I have searched the archives on here and cannot find any details on it. |
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Personally, I'd rethread just to be 100% sure that the threads are concentric. A really sloppy thread will work fine for a flash hider - not for a supressor. When barrels are threaded in production, the thread is cut relative to the barrel's diameter. They are not centered on the bore. This can be close, or it can be off by enough to be troublesome.
When threading for a silencer, the bore is carefully measured and then the threads are cut concentric to it. Equally important is thh shoulder in the barrel, it must be cut perpendicular to the bore. In practice, it's usually easiest to cut off the threaded end and start fresh. If you think your barrel is at the legal limit, measure it carefully. I have found 9 out of 10 barrels can be trimmed and rethreaded and still satisfy length requirements. Of course if you do happen to come up a little short, you can permanently attach a QD flash hider, or even the supressor itself. No issues there. Just a few weeks ago I had a 14.5" barrel in here. Cut the OEM thread off, rethreaded, added the QD flash hider, and it still came out at 16.25" |
| I have a bushmaster upper on my AR and shot it with my 7.62 YHM phantom with no problems. Granted using the 7.62 can might make it a bit more forgiving... Don't think I have ever read much specifically bad about the threading on a bushmaster barrel. At the very least I'd sight down it and make sure that the barrel looks smaller than the opening in the can although I guess that probably isn' the scientific approach though. |
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One other thing - by rethreading you'll reduce or eliminate the POI change from supressed to unsupressed. POI shift is largely caused by asymetric gas blowing around the bullet. This happens when the bullet doesn't go right down the middle of the bore. If the bullet is dead center, there is about .030" between it and the baffles. Now shift the bullet so it is no longer on center, .040" on one side, 0.020" on the other. More gas coming around one side serves to push the bullet a little bit. A little bit of push at each baffle....
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Quoted:
All good information guys, thanks. I need to measure my barrel because I do not want to permantly attach anything to it. Who do you guys recommend to thread my barrel? ADCO firearms. If you can remove the flash suppressor (you'll have to to connect the AAC mount) use a set of cheap digital or dial calipers and measure the barrel all around to see if it is concentric. It will save you having to send it anywhere. |
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Quoted:
Quoted:
All good information guys, thanks. I need to measure my barrel because I do not want to permantly attach anything to it. Who do you guys recommend to thread my barrel? ADCO firearms. If you can remove the flash suppressor (you'll have to to connect the AAC mount) use a set of cheap digital or dial calipers and measure the barrel all around to see if it is concentric. It will save you having to send it anywhere. Calipers are not exactly suitable for measuring for concentricity. Regardless, any good, competent shop can get it concentric enough that you would never be able to tell. |
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