muzzle thread question

D

dadonkey

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Hi all,
I hope this is the right place.

For my Stag 10 build I have a 6.5 CR barrel made by BCA (I believe). I bought it off a friendly CGNer, but it has no manufacturer name stamped on it.
Thread is 5/8-24 (verified with calipers and thread gauge).
I bought a muzzle brake with the same thread specification (also measured when it arrived to be sure).

The problem is that it will thread less than 1 full turn by hand, and I obviously don't want to reef on it and damage the threads irreparably.

On close inspection the threads on the barrel don't have a nice chamfer at the muzzle, and the first turn from the muzzle end has a slight imperfection. The flank of that thread (see picture here) is a bit fatter, like the tool that was cutting it snapped off just before it got to the end.

Is this a common problem?

What's the best way to fix this?
I don't have a die for 5/8-24, and they're not terribly expensive on Amazon, but using taps and dies is one of the few things that stresses me out.
Should I attempt with a triangle file?
 
Not a common problem. Usually threads are cut to spec.
A die stresses you out, but you are prepared to attack the barrel threads with a triangular file?
 
See if you can find a 5/8x24 split die?

You can start the die back by the shoulder and turn it off towards the muzzle end.
 
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Thank you both for the advice.
I didn't know split dies existed. Unfortunately not easy to find.
I see your point about the file. I definitely don't want to do a hack job. Just trying to do the least hacking possible :)
Given that the brake does thread on 1 turn I probably have a good chance of doing minimal damage with a regular die.
 
You can get a Thread Restorer Die (rethread die) from local bolt supply shop. They don't double cut the threads and thin them out.
 
There are thread files. Basically a square file and each side has grooves for different thread sizes. I got mine from snap on but i think you could get one a princess auto. No dies or triangle file needed. A few passes and she should spin right on.
View attachment 358795

There are 4 sizes on each end and the red handle slips off to be installed on either end. Available in metric and sae. I think mine was under $20

These are great for minor repairs especially on the first thread where its hard to start a die.
 
is your barrel stainless or black?
sometimes stainless threads tend to pack up rather quickly when jammed tight with say another brake from previous owner? i would chase with die before ever filing myself
 
OP, Sounds like you are in for some fun. On a lathe, the chuck is to your left. Top of it turns towards you. So, a cutting tool for cutting threads starts to the right of work piece and travels left. In other words, lathe cut threads start at muzzle and travel towards chamber. A die has two sides, only one is the leading edge. Can only be correctly used by starting the cut with the leading edge. With right hand threads, that means die also starts at muzzle and travels toward chamber end. "Split dies" are for adjusting depth of thread being cut. Your assessment that " like the tool that was cutting it snapped off just before it got to the end." might be based on the assumption that threads are cut on the barrel starting back somewhere's and emerging at the muzzle. Would require lathe running in reverse and cutter upside down, and then some other adjustments to get threads deep enough to spec. Maybe your barrel got threaded that way??
 
Why not simply take it all to a gunsmith and have him determine if the brake is 5/8 x 24 and if it is, thread the barrel properly...
 
Thanks for all the advice.
I'm a DIY guy - the kind that hates taking a car to a mechanic if I can do the job myself.
So I got a simple suggestion from a mechanical engineer friend for a setup to mill a 45 degree chamfer that solved the problem. I simply ended up rotating the barrel slowly (a few RPM) from the chamber end with a Dewalt drill and supporting the opposite end with a bearing, while I lightly held a Dremel spinning a sanding disk up to the start of the threads (at said 45 degree angle).
A few turns of the barrel and that was it. Muzzle brake threaded on without effort.

I finally figured out how to add photos.

Original problem with the first threads:
uc


How I supported and rotated the barrel while I ground the chamfer:
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Here you can see the chamfer, albeit out of focus (shiny):
uc
 
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