Uuggghhh... possible for a brake mount to cause keyholing?

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pneumagger
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Uuggghhh... possible for a brake mount to cause keyholing?

Post by pneumagger » Sat Dec 07, 2013 9:23 pm

So I put together a 14.5" .308 AR and took it out for the first time today after checking the headspace. All parts are brand new and it cycles well. I visually checked the suppressor alignment looking down the bore a couple days ago, it looks perfectly centered - so the brake must be well-aligned and looks perfect. I took a few shots without the can and the brake really takes the jump out of the rifle all by itself. It took about 10 rounds or so get the adjustable gas block dialed in and went to sight it in on paper.

I tried 168gr Hornady A-Max and 147gr PMC and had keyholing every shot at even 7-10yds. It must be tumbling right out of the barrel. I was shooting without the suppressor and I see no evidence of bullets touching the brake mount. See pics of all angles of the brake... no strikes.

There is about 1/2" from the muzzle inside the brake until the first brake chamber opens up. Could there be still be so much pressure/powder that the bullet is being destabilized in the brake? The fireball is impressive. The brake is pinned, so I'm not sure what my next step is. (?)

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doubloon
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by doubloon » Sat Dec 07, 2013 11:54 pm

I guess anything is possible but I don't see how.

Really can't help you but I just wanted to comment I have never seen such perfect keyholes.
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by MJF1911 » Sun Dec 08, 2013 12:03 am

Does the barrel have rifling? I've seen factory new barrels with no rifling.

Have you checked the twist rate? Use a tight patch on a cleaning rod to measure the twist.

Have you slugged the barrel to check its diameter?
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by pneumagger » Sun Dec 08, 2013 1:09 am

The bore and barrel look beautiful. Headspacing is great, there was no excessive fouling or overly shallow lands and I can't drop (or push) a .308 bullet down the bore with a rod... plus it must seal well enough to cycle great. I don't see how it couldn't be a .308 bore. I never thought to try measuring the twist though. I'll give that a look.
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by rimshaker » Sun Dec 08, 2013 2:39 am

Standard twist rate for 308 is 1:12 inches. 14.5" is a pretty short barrel for 308. Definitely won't be shooting next to you at the range :mrgreen:

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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by eastern_hunter » Sun Dec 08, 2013 9:17 am

Although something appears to be wrong ... you might try several more bullet weights both heavier and lighter. Looks like it would be good to say a prayer or two as well.

Sure would not put a can on that rifle yet!!!

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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by twodollarbill » Sun Dec 08, 2013 12:03 pm

I too have never seen a target with perfect keyholing like that. :roll:
I've been lucky and never had a problem with a factory length barrel.
On Ruger 10/22 barrels that I have cut down I have had a couple keyhole problems
but recrowning the barrel has always corrected it.....but that was 22lr.

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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by rjacobs » Sun Dec 08, 2013 2:56 pm

I assume thats the AAC 51t Brake?

If so I run one of those on a 16" LMT MWS and have zero issues across a wide range of ammo(150g FMJBT, 155g Noslers, 168g SMK's from various manufacturers, 175g SMK's from various manufacturers and hand loads).

Only thing I can think is possible de-stabilization from the muzzle blast, but as I understand it thats pretty rare.

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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by redtazdog » Sun Dec 08, 2013 3:12 pm

Check the crown as there could be a burr on one side or something that is kicking the bullet off as it leaves
the barrel.
If the bullet is getting a small kick because of a bad crown chances are it may be only off a hair going through the
flash hider but if its .001 at 1/2 out of the bore it will be ten + times that at 10"
If the bullet is set in motion to go sideways it will.
Would be much easier to re crown and test shoot again without the flash hider but in your
case you will need to be creative to re crown it with it pinned on.
I have a pile of barrel stubs from factory barrels with crappy crowns, some you can see the crown is a 60 degree
cut for a live center.
They give a barrel blank 60 degree cuts on both ends and do most of the barrel work and leave the cone cut on the muzzle end thinking it will work as a crown even after the center has been pressed against it. :roll:
No tools should touch the muzzle after crowning.
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by MJF1911 » Sun Dec 08, 2013 3:32 pm

I'm thinking when they cut your barrel and pinned and welded that comp they distorted the muzzle. You'll know for sure if you slug it as you'll feel the constriction easily.
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by redtazdog » Sun Dec 08, 2013 3:37 pm

MJF1911 wrote:I'm thinking when they cut your barrel and pinned and welded that comp they distorted the muzzle. You'll know for sure if you slug it as you'll feel the constriction easily.
I have seen this too
I use these for checking the crown and if any fuzz hangs on the end of the muzzle crown when pushed through the bore
then the barrel crown/muzzle has a burr.
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by Grounded » Sun Dec 08, 2013 3:54 pm

What twist does that barrel have?
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by 57fairlane » Sun Dec 08, 2013 6:39 pm

Guys are on the right track so far . . .

The AAC brake is a proven design, something else is amiss here.

Either the crown, alignment issue on the shoulder or if you cut down and pinned/welded on a button-rifled barrel it could present a stress relieving issue out there on the threads/crown area.

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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by Pman5KMO » Mon Dec 09, 2013 11:00 am

57fairlane wrote:Guys are on the right track so far . . .

The AAC brake is a proven design, something else is amiss here.

Either the crown, alignment issue on the shoulder or if you cut down and pinned/welded on a button-rifled barrel it could present a stress relieving issue out there on the threads/crown area.
Or while being drilled for the pin they created a burr just prior to the muzzle which will screw things up as well....
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by pneumagger » Mon Dec 09, 2013 9:53 pm

I contacted the barrel mfg and they said they'll take a look at the whole upper. I figure that best case scenario, I'll just have to get a new 51T brake...worst case scenario, I'll just end up buying a new barrel (from elswhere), too.
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by 66427vette » Mon Dec 09, 2013 10:19 pm

Who made the barrel?

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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by Wildfirescott » Thu Dec 26, 2013 11:42 pm

Please let us know the results of their investigation.
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by Emilio » Fri Dec 27, 2013 12:58 am

My guess is barrel or crown and this is short for .308!
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Re: Uuggghhh... possible for a brake mount to cause keyholin

Post by 57fairlane » Tue Dec 31, 2013 9:25 am

Emilio wrote:My guess is barrel or crown and this is short for .308!
:mrgreen:

14.5" in .308 is hell on any can.

There's been a few issues with suppressing the 12.5" HK417 since that seems to be a hot item nowadays.

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