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Posted: 11/18/2013 3:56:10 PM EDT
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I've tried elsewhere for help, now I'm going to try here. I'm installing an AAC Blackout 1/2x28 51t mount onto a BCM barrel. This barrel previously had an AAC 18t flash hider on it which worked fine.
I have called AAC. Shorty story is, I got the run around. The guy tells me that its ok to seat the mount on the muzzle, and he also claimed that my threads were out of spec. Therefore, it's on me to send my barrel off to cut the threads if needed, and recrown, in order to fit the barrel to this mount. First of all, he kept referencing a drawing that is for pistol threads. Here is that drawing: 
Now, this is an application that should use the drawing for M4 style rifles, shown below: 
There are a couple things to note here. The pistol drawing states "this thread profile can shoulder against the muzzle face or behind the threads." That statement does not appear on the M4 drawing. This would seem to indicate that for M4 style barrels, the mount should not seat on the muzzle. Ok, so that might not be enough to go on. So look at the pistol drawing and it indicates a requirement to hold the shoulder perpendicular to the bore if you want to seat on the shoulder, then it indicates a requirement to hold the muzzle face perpendicular to the bore if you want to seat on the muzzle. Now, look at the M4 style drawing. It only indicates a requirement to hold the shoulder perpendicular to the bore, but there is nothing about the muzzle face. To me, that confirms that the mount should seat on the shoulder. The M4 style drawing also says "this thread profile is compatible with all AAC muzzle devices". So, I have an AAC muzzle device. My threads are to the drawing. The drawing is saying the muzzle device should seat on the shoulder. Yet it comes up way short of that, instead seating on the muzzle face. The mount I have here allows 0.577" of thread length before seating on the muzzle. What am I missing? I tried contacting AAC but their guy really didn't seem to know what was going on and I'm completely skeptical of anything he told me. According to him I should do one of the following: -recrown the barrel and seat on the muzzle -cut the barrel down enough to seat on the shoulder and recrown -find another mount like the others I have that work fine I have a problem with all of these options. Thoughts? |
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Quoted:
perhaps you need some shims  Why would I need shims when the threads are exactly per their own drawing? I have several other AAC flash hider mounts that were apparently made correctly and seat on the shoulder. ETA: I don't have the means to machine a proper shim. And I'm not going to stack shims for this. |
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I've got some these on the way to take care of this issue.
http://precisionarmament.com/products/accu-washer-system/ |
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So, they sell different variations of the same mount under the same part number. Even if you have your threads cut to their drawing its still a crap shoot as to whether the mount will fit. Nice.
I thought after the 18t debacle I was going to be safe with the 51t stuff. Apparently not. I'm getting ready to get another can, so I guess this makes up my mind regarding which brand I won't be buying this time. Three AAC cans is more than enough BS for me. It's nice to know that somebody sells something that may fix the problem, but when my threads are to the drawing I'm not willing to spend more to fix it. Yeah, its not that much, but I've just had enough of AAC bullshit. I'll just sell this mount and move on (at least I have two 51t mounts that work). Any AAC fan boys wanna step up? 
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| Why do you not want to stack shims? That is what you are supposed to do. I have a Breakout on a BCM barrel. I used 2 shims to time the ports. The mount will bottom out on the barrel shoulder if I did not use the shims. I had to use shims for the break mount too on another AR. I have seen AAC state before that it was ok for the mount to rest against the muzzle. |
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Quoted:
Why do you not want to stack shims? That is what you are supposed to do. I have a Breakout on a BCM barrel. I used 2 shims to time the ports. The mount will bottom out on the barrel shoulder if I did not use the shims. I had to use shims for the break mount too on another AR. I have seen AAC state before that it was ok for the mount to rest against the muzzle. This isn't a brake, it's a flash hider. I have brake mounts, and they are timed with shims. If it's ok to seat against the muzzle, why does the thread guide indicate otherwise? My muzzle isn't squared up with the bore, and according to the drawing it doesn't need to be in order to work with their muzzle device. I've not seen AAC state this is ok for a 1/2x28 mount on a rifle barrel...not in their documentation or otherwise. Where did you see AAC actually state this? If you have them as the source, I'd like to see it because obviously it contradicts everything I have shown here. |
| I think I read it on Silencertalk. I have not been on that forum in quiet some time, so I really can't be sure. I missed that it was a blackout. I read it as breakout... I understand you being pissed. Did you measure the length of the threaded portion of the barrel? |
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Quoted:
I think I read it on Silencertalk. I have not been on that forum in quiet some time, so I really can't be sure. I missed that it was a blackout. I read it as breakout... I understand you being pissed. Did you measure the length of the threaded portion of the barrel? Hearsay isn't good enough for me on this. If I get a baffle strike or something, they're going to whip out their drawings and claim that I should have followed them (and the drawing is clearly calling for muzzle devices to seat on the shoulder). Again, the threads are to the drawing. I determined that by measuring. |
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