Barrel integrity still ok?

[Quizcat]

I used a pipe thread cutter to remove a 1/2" long barrel shroud from in front of the front sight post of a Saiga 7.62 x 39mm Rifle barrel, in order to thread the end of the barrel for a muzzle device. The Saiga Rifles don't come with muzzle devices, and mine didn’t have threads pre-installed, so you have to thread the end of the barrel yourself.

The muzzle device calls for a 14 x 1LH thread. When I removed the barrel shroud, the tube cutter wheel did cut into the OD of the barrel slightly deeper than the depth of the shroud itself. The groove around the OD of the barrel is probably about the width of a dime.

The barrel diameter mics out as follows:
Barrel diameter =.565”
Diameter of the Tube Cutter Groove = .489”

So, the difference between the OD of the barrel diameter and the OD of the groove diameter = .076”

A 14mm x 1 thread has a .497” (thread minor diameter), so when you factor-in the.489” (Tube Cutter groove diameter) that equals .008.” So, I should have about .008” of excess barrel material above the minor diameter of the threads.

So, will cutting accidentally into the barrel slightly with the tube cutter affect the integrity of the barrel?

I assume the pressures at the end of the barrel would be significantly less by the time the gases are expelled through the piston mechanism, etc. I also assume the muzzle device itself will provide quite a bit of additional strength when screwed down and completely covering the tube cutter groove. I’ll be using some Rockset to secure the muzzle device to the threads so the muzzle device doesn’t move.

[FrankenMauser]

Anything that 'squeezes' the barrel - especially things that imprint upon the barrel - can cause a bore constriction.
Bore constrictions are rarely conducive to peak performance.


How did you ensure that the threads were cut concentric to the bore?

[Quizcat]

The threads have not been installed yet, but I am going to be using a 7.62 x 39mm arbor that fits perfectly into the ID of the barrel, acting as a guide for the die. The arbor has a 14mm x 1mm male thread on the other end, which is then threaded onto the ID of the die. So, the die will be perfectly perpendicular to the bore when the die cuts the threads.

There isn't any restriction introduced to the bore. It would seem to me that if the mistaken groove I cut around the periphery (OD) of the barrel to remove the barrel shroud is still going to be 008" greater in diameter than the bottom of the threads (the minor diameter of the threads), which I'll eventually cut in OD of the barrel, that I would be fine. But, I'm not a gunsmith.

[Scorch]

Barrel diameter =.565” Diameter of the Tube Cutter Groove = .489”

That .076" groove would concern me because pipe cutters cut by squeezing.

Anything that 'squeezes' the barrel - especially things that imprint upon the barrel - can cause a bore constriction.

Exactly. And a bore constriction will cause accuracy and pressure issues.

There isn't any restriction introduced to the bore.

How do you know? Did you slug the bore? Bore micrometer? Plug gauge? Until you know for sure, don't just make assumptions about it.

But, I'm not a gunsmith.

Already figured that out, thanks. And don't get me wrong, I have people bring stuff in all the time that they are working on and damaged the firearm, but the idea is to do the work without damaging the firearm or causing a hazardous condition.

[Quizcat]

I did thread the end of the barrel with the 14 x 1 LH die. The depth of the tube cutter groove is completely obliterated by the new threads. I used a guide arbor on the die to make sure that the threads were installed perpendicular to the bore of the barrel. The die's arbor guide didn't bind whatsoever in the bore as I was installing the threads.

The cutter groove itself only extended .500" back from the end of the bore, and the arbor extended at least 1.5" into the bore, at least an inch beyond where the cutter groove on the OD of the barrel was located. Of course, cutting into the OD of the barrel was not something I planned on doing. I don't like it, I don't recommend it, etc...but it happened.

I guess I can mic the bore. It doesn't seem like there would be a bore constriction from "cutting" .008" into the OD of the barrel with the tube cutter, just based on the arbor turning so freely in the bore.

I realize that testing for bore diameter changes isn't going to conclusively establish whether there was a constriction established just based on the die arbor guide turning freely. So, just to be safe, I'll mic the bore, and report back whether cutting .008" into the OD of the barrel caused any constriction in the bore.

I'm more concerned about whether safety was compromised with respect to the groove in this case, versus issues of accuracy being perfect. We're talking about an AK47 here, Russian made, and I'm not expecting to get one or even two MOA from it. That doesn't mean I want it to be inaccurate, no, but just sayin'...

[Quizcat]

Upon closer inspection, I didn't feel that the threads actually sufficiently obliterated the groove as I initially thought. So, I ended up using some "Higher Strength" JB WELD in the groove. The "Higher Strength" formulation provides slightly over 5000 psi of strength added in the groove. I figured that it would fill in the gap between the reduced barrel OD at the groove and the muzzle brake, filling up the void that would otherwise be caused by the barrel groove without any filler. Then, with the muzzle brake screwed tightly in place, I theorize that the muzzle brake would also add to the strength of the barrel at that point, since the body of the muzzle brake would be covering the JB WELD filled gap completely. I'm using a Tapco AK bird cage muzzle brake. It's made to resemble the AR15 bird cage, but the bore is for the AK round. It's beefier than most muzzle brakes, about 2 ounces, which is not typically desireable with respect to adding weight to the rifle, but in this case, I theorize that the benefit of the beefy muzzle brake will serve to add strength to the barrel at the groove.

The photo attachment entitled "groove 1" is the original groove in the barrel, after the threads had been installed, and the photo attachment entitled "groove 2," is of the groove filled with JB WELD High Strength epoxy.


Please comment on whether you believe JB Weld High Strength will be beneficial, a detriment, or of no additional benefit?

[Bart B.]

This barrel is squeezed down a bit by the band holding the front sight.

https://www.flickr.com/photos/[email protected]/4351857940/

No accuracy loss at all.

[Quizcat]

Good point, and the groove is about 1" past the front sight block. I'm hoping too that the pressures, by the time they reach within .500" of the end of the barrel, would be substantially less to the extent that a groove in that location would have little or no effect upon safety as well.

[Jim Watson]

A groove half an inch from the muzzle is not a hazard. The epoxy is not doing anything for it.

[TX Nimrod]

Agreed, the “high strength” epoxy is compressible so the only thing it does is make removal of the muzzle device more difficult.


.

[Quizcat]

Well, I haven't installed the muzzle break yet. I let the JB WELD fully cure in the groove first, and will use some Rocksett on the threads as a thread locker, so the muzzle brake doesn't work loose over time from the rifle is being fired.

Do you mean that once the brake is installed over the cured JB Weld in the groove, that the JB Weld will change consistency to the point that it might make the muzzle break more difficult to remove?

[4V50 Gary]

If you need JBWeld, you're doing it wrong.

First, I would have cut the threads on a lathe. Second, who made that muzzle brake? If it's the one Saiga comes with normally, then it's already been engineered for the thread depth and pressure. If it's aftermarket, I'd go with another one.

[Quizcat]

I accidentally cut into the OD of the barrel in order to remove the barrel shroud. It's not something I planned on doing. But, threading for a muzzle break on a Saiga conversion has been successfully done this way thousands of times.

Saiga rifles never came direct from IZHMASH in Russia with muzzle brakes, so any that would be selected are going to have to be after-market. Saigas take any of the commercially available muzzle brakes that have 14 x 1LH threads., the same as a standard AK47.

The lathe is technically the "right" way to do it, but I can't justify it, not on an already assembled rifle.

[Quizcat]

Upon close inspection where the groove in the OD of the barrel was cut I noticed an anomaly on the ID of the bore, right where the groove on the OD had been cut. It appeared to be more of a concentric crack in the barrel all around the ID of the bore exactly where the groove had been accidentally cut through the barrel shroud and into the OD of the barrel. The .300" pin gage still cleared the bore, but there was some scraping along that "crack" in the ID of the barrel.

So, rather than chance it, I decided to cut off the 1/2" of the end of the barrel where the groove had been cut, reface the barrel to 90 degrees, then recrown the barrel to 11 degrees, just like the original. Now, a .300" pin gage drops all the way down to the breach, slick as a whistle, totally unobstructed.

Next, I'll use a hollow mill to remove what's remaining of the barrel shroud in front of the front sight block, about .500" long, then thread it for a muzzle brake. I'll be using a guide arbor on the thread die so the threads are sure to be concentric with the bore.

I'm about .250" short of the required 16" barrel length after removing .500" off the end of the barrel. So, I plan to permanently attach the muzzle brake using silver solder so that the overall barrel length will be in compliance with the muzzle brake permanently afixed to the barrel.

I'll need to obtain an MAPP torch, and some high temperature silver solder (minimum 1100 degree) in order for the installation of the muzzle brake to be within compliance. I've never had to silver solder a muzzle device before, but think I'll prefer it to a pin and weld method with respect to aesthetics.

With the refacing and recrowning completed, is there any reason to test fire the rifle for accuracy and function before I remove what remains of the barrel shroud in preparation for threading the barrel for the muzzle brake?

Any pointers on silver soldering the muzzle break?

[44 AMP]

Test fire for function, ok
Test fire for accuracy? waste of time.

Additional cutting and addition of a muzzle brake will almost certainly change the accuracy, so testing it for accuracy before you are finished is a waste of time.

Do note that silver solder, (done correctly) is not actually permanent, but is "permanent enough" to satisfy the ATF.