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Old December 3, 2009, 10:18 AM   #1
spencerhut
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AR Barrel (DPMS) thread problem

So I was helping a buddy build his first (civilian) AR last night and when we took the muzzle brake off to install a low profile gas block it seemed harder than normal to get the brake off. I thought it was Locktite, but it was not. Look carefully at the image and you can see an almost perfect round deformation in the threads, like the barrel was drilled and filled with a dissimilar metal?


I was going to get a 1/2-28 die and clean it up, but thought I should mention it here first to make sure I'm not missing something.

BTW - I have the exact same part number barrel on my wife's AR and we did not have this issue with it.
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Old December 3, 2009, 12:48 PM   #2
Scorch
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Looks like the threads have been damaged by either a) crossthreading the brake, or b) incompletely cut threads in the muzzle brake. Either way, the thrads have been damaged.
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Old December 3, 2009, 01:36 PM   #3
spencerhut
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Nope, that is not it. Looks like the threads in all but this one spot are perfect. This one spot has been drilled, before or after threads were cut in the barrel, and another metal welded / inserted in the hole as a means of retaining the muzzle brake.
I think.

Just wondering if anyone had seen DPMS do this before.
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Old December 3, 2009, 01:54 PM   #4
edward5759
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retaning screw

The last post was correct
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Old December 3, 2009, 01:56 PM   #5
DBAR
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Was it bought by your friend "New"? If so, a call to DPMS is in order. It may have been a "Post Ban" barrel that they changed over to fill new orders. I wouldn't think they'd do something like that, but you never know. If he bought it used, then someone may of had a Permanent muzzle device removed.

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Old December 3, 2009, 02:18 PM   #6
edward5759
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hit the wrong button

The reason is stated above, spencerhut is right.

It was drilled or you have a retarding screw that you didn’t loosen before you took the brake off. If you notice the last four screw threads they are compressed downward, thread points are no longer sharp!
This is from the screw dragging across the top of the thread.

In the future when you have a retarding screw that rests on the threads, I will place #9 or #11 shot of lead in the hole then screw down.
Almost like a reloading die lock ring from RCBS.
Just grind a little off of the screw so it will sit flush.

Chase the threads with a die, if it’s a slotted die make sure that it is not to tight or your female end will have too much play. Only clean up the first four threads!

Good luck with the project ed
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Old December 3, 2009, 02:22 PM   #7
spencerhut
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The brake on this gun has no provisions for a retaining screw. None, it is retained by the barrel nut only.

This was brand new from MidwayUSA. No signs of tampering, looked perfect on the outside.
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Old December 3, 2009, 02:40 PM   #8
edward5759
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threads

The threads probably are a pipe thread at the end. This is from backing off the cutting tool on the lathe as the threading process is ending.
This too will give it a compression fit.
Still I would only chase the first four threads, no more.

Ed
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Old December 4, 2009, 09:14 PM   #9
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My guess is that the brake was permanently pinned to the barrel at the factory. When you wrenched off the brake, the pin smeared the threads.

Pinned brakes are done as a way to permanently attach a muzzle brake. This is done to comply with local laws that prohibit flash hiders or because the barrel is shorter than 16".
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Old December 18, 2009, 01:23 AM   #10
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Finally got the 1/2-28 die in the mail today. All fixed in 5 minutes.
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Old December 18, 2009, 02:38 PM   #11
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DnPRK is dead on. That barrel had a permanent flash hider mounted on it. You drill through the hider into the barrel, pin and weld it. If that barrel is under 16" you are breaking the NFA laws until you weld another hider on.
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Old December 18, 2009, 06:40 PM   #12
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If you read the entire post, I have two of these, both are 16" w/o the muzzle brake. There is zero evidence the muzzle brake has been drilled or welded. I looked closely inside the muzzle brake. I'm no expert, but this is not my first rodeo either. The entire point of this thread was I found something strange. I can ID pins and welds, this was neither, that was why I asked.
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Old December 19, 2009, 04:14 PM   #13
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DnPRK is dead on. I repeat-dead on.

That brake was pinned on. No question about it. You can tell by looking at the pic. You can see the circumference of the 'sheared' pin just by looking at the pic. If it was a thread problem they would be 'galled' right from the start & you'd have a hell of a time getting the brake off-plus it would've ruined the barrel threads. Good thing there was anti-seize on the threads when they installed it.
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Old January 11, 2010, 11:29 PM   #14
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Pinned and welded to be sure. Some states still mandate the "Permanently secured muzzle device".
They are pretty easy to spot if you know what to look for. Before you go tearing out the wrench next time take some time and examine the Muzzle device really well. Usually you will find a spot that is slightly discolored or has sanding/file marks. Take a file lightly to that spot. You will typically find that it is harder than the surrounding metal. That is why the finish looks different. Parkerizing will take differently on different hardness/alloys.
The way I deal with them is via the mill.
A 1/4 or 3/16th" carbide mill will chew through the hardest weld bead. Once you get through the weld the pin will usually start to spin in its hole. I have always been able to blow them out or pluck them with a magnet at this point.
Remove muzzle device as normal.
If you dont have a mill then careful use of a die grinder with a carbide burr or stone will suffice.
Forget a drill press and drilling it out. You will just burn up HSS bits (How did I know that?)
BTW- The only time you have to worry about permanently securing the muzzle device is:
1- You live in one of the states that still has a ban in effect.
2- The barrel is less than 16" without the device. At that point you need to install a device and permantly secure it so the total length is in excess of 16"

There are 4 methods of "Permanently securing a Muzzle Device" that is acceptable to the BATF:
1- Fusion weld no less than 180 degrees around the circumference of the device.
2- 4 equally spaced tack welds around the circumference of the device.
3- Silver Soldering with a melting point of 1100 degrees or more.
4- Blind pin and weld pin by fusion welding.
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Old January 12, 2010, 12:11 AM   #15
gyvel
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Can't anybody read? The man said there is NO evidence of a pin or a set screw in the muzzle break. And he certainly sounds like he knows what he is talking about.
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Old January 12, 2010, 02:11 AM   #16
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Let's see the Muzzle break.

I'd like to see a picture of the muzzle break. Top, bottom left and right side.

It can be REALLY hard to see the pin in a muzzle break that has been done "correctly." It may even be "impossible" to do so once you've "machined" the pin by forcing off the hard steel barrel. The Park Color difference that HockeySew mentions may be the only "giveaway" at this point. I have one and I didn't know it was pinned on until I compared it to another that was not. My barrel is only 14.5" with a 2" muzzle break permanently attached to comply with FEDERAL LAW. When it's standing side by side with a 16" barrel with a standard A2 Muzzle Break, they look almost identical. (Other than the different muzzle breaks.)

Measure the barrel from the face of the bolt to the end of the barrel (using a cleaning rod to mark the distance.) If it's less than 16", then OP will know for sure that he just made a rifle into a "short barrel rifle" accidentally.

To be legal, the muzzle break needs to be permanently re-attached to comply with the 16" minimum-barrel-length federal law.
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Old January 12, 2010, 11:08 AM   #17
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Quote:
Can't anybody read? The man said there is NO evidence of a pin or a set screw in the muzzle break. And he certainly sounds like he knows what he is talking about.
How does he know that is th eonly muzzle break ever attached to the barrel?

We are trying to tell you that at some point a pin was used to effect a permanent muzzle break attachment.

It has been removed, the hole filled, and the barrel threads cleaned up (partly).

The fact that the muzzle break he now has is not drilled just means it is not the original.
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Old January 13, 2010, 04:45 AM   #18
gyvel
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Quote:
How does he know that is th eonly muzzle break ever attached to the barrel?

We are trying to tell you that at some point a pin was used to effect a permanent muzzle break attachment.

It has been removed, the hole filled, and the barrel threads cleaned up (partly).

The fact that the muzzle break he now has is not drilled just means it is not the original.
You've got a point there. Never thought of that.
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