Gunsmithing Thread chaser for muzzle threads

[atombomb]

I have a barrel with a small ding right on the starting muzzle brake thread… I tried to start a muzzle brake on it to chase it or clean it up some, but there is not enough to get it started and me comfortably put any pressure on it… since I shoot suppressed, I need to clean it up and not affect the alignment of the can to the bore… Anyone have any thoughts or recommendations on a tool that would work? Or should I just file that one spot down?

 

[spife7980]

Custom barrel that the smith would refuse correcting because you filed on it? If so ask him.
If not and you have a file, that’s what I would do. Slowly. Carefully.

 

[iceng]

Thread file is what you seek. The have a bunch of thread pitches on the one file. Cheap and work well for quick repair of dings.

 

[atombomb]

Thread file is what you seek. The have a bunch of thread pitches on the one file. Cheap and work well for quick repair of dings.

Thanks, I had looked at those, but wasn’t sure if those pitches worked with the threading, isn’t it 2A or something special? But I’ll order one and give it a shot… gotta be better than a flat file...

 

[LeftyJason]

Thanks, I had looked at those, but wasn’t sure if those pitches worked with the threading, isn’t it 2A or something special? But I’ll order one and give it a shot… gotta be better than a flat file...

2a or 3a is the tolerance class of OD threads not profile shape. 2b or 3b is internal threads. UN shape is what you seek unless it is metric. 3's should always fit on a 2 or a 1, not necessarily the other way around.

To get different shapes (which you are not going to get into in guns) would go to something like a UNJF, UNJEF, or UNJS. The J stands for a different root radius, generally bigger. C is for course, F for fine, EF Is for extra fine. The S stands for a special size. Today at work we are grinding a 3.4980-24 UNJS-3a left hand thread. I also grind 1/2-28 UNJEF 3a and 9/16-18 UNJF-3A as well. All the threads I girng are in inconel. Aerospace turbine jet engine stuff.

 

[strikeeagle1]

You need to use a split die that can be applied beyond the faulty threads... I have a number of these for gunsmith use.
An example of what you need, just get the muzzle thread size.

 

[ma smith]

https://jawco.com/collections/thread-restoring-files/products/3-rethreading-file-set

 

[Huskydriver]

Thread file or a die as recommended above

 

[n2ishun]

Those thread files are for shit.....ask any mechanic that has had to use one twice, you'll find they didn't work either time.

The split die will work much better but since the *dink* in the threads is right at the tip of the barrel it might not do the job you want.

Swiss needle file is what you're looking for, with lots of patience and some care it will do what the others won't.

 

[lariat]

Using a standard triangle file would be my last choice. Too much chance for error in over-filing or getting it angled in an odd way. Either of the options above would work much better.

 

[iceng]

Those thread files are for shit.....ask any mechanic that has had to use one twice, you'll find they didn't work either time.

I reccomend them because I use them with great success.

Some even have a spike on the end for repairing internal threads, which I often do. Yes taps and die nuts work better, but in a pinch, and for a few dollars, they work fantastically.. for me.

 

[ma smith]

It really depends on the damage. I've repaired muzzle threads using a thread file, just fine.

 

[XLR308]

I've had one barrel with a similar issue.
I have jewelers/needle files and allsorts of other file shapes including a set of snap on thread files.
The thread files worked perfectectly and are the least aggressive of the assortment when it comes to cutting and material removal.

 

[lariat]

It really depends on the damage. I've repaired muzzle threads using a thread file, just fine.

for sure it can be done. I have way too much experience in this area, and I’m seeing something on those threads in the OP pic that I think needs to be considered:

There are three places where the threads are goobered. If you use a regular file by hand you will naturally rotate the file into the other threads that are not damaged and use them as a guide and they will be filed as well. So the opposite thread that is not damaged will get cut down also. You want to avoid this as much as possible. For a coarse thread used for general purpose is a non issue, but those are 1/2-28 - machine threads. So it would be best to use the appropriate tools for the job, and they are relatively cheap.

I’m not saying it can’t be done. But the use of the threads and the detail of the threads should be considered, especially if they will be used frequently. Pitch is important, and both of the options above take that into consideration more than a regular file would.

 

[45-90]

You need a lathe...the muzzle face has a ding. The thread relief has a ding, and threads are dinged in a couple places...
A file is not the correct tool for this job to achieve a desirable outcome.
But you could use a die, if its say 1/4 X28, lube with heavy cutting oil, mount in a lathe tailstock die holder will center your indicated barrel. Start by hand with pressurre to get the die to cut away the dinged up part.
The die can be used by hand but if ya don't have some experience with it, getting it started straight can be a problem....the lathe makes perfect alignment, and recommended.
So now, it will thread on your muzzle brake...
But the barrel face is dinged...so face it off...and back to the lathe to do it right. Check for excessive rounout, especially if done by hand. Sloppy thread, and unsquare mating surfaces, force the brake to one side.
Your choice.

 

[LeftyJason]

You need a lathe...the muzzle face has a ding. The thread relief has a ding, and threads are dinged in a couple places...
A file is not the correct tool for this job to achieve a desirable outcome.
But you could use a die, if its say 1/4 X28, lube with heavy cutting oil, mount in a lathe tailstock die holder will center your indicated barrel. Start by hand with pressurre to get the die to cut away the dinged up part.
The die can be used by hand but if ya don't have some experience with it, getting it started straight can be a problem....the lathe makes perfect alignment, and recommended.
So now, it will thread on your muzzle brake...
But the barrel face is dinged...so face it off...and back to the lathe to do it right. Check for excessive rounout, especially if done by hand. Sloppy thread, and unsquare mating surfaces, force the brake to one side.
Your choice.

If you use the thread file carefully it will barely be off. Take a normal fine file (if it needs it) to touch up the corner ding. Besides shouldn't the muzzle brake be indexing off of hm... I don't know. Maybe the shoulder at the back of the thread?

 

[45-90]

It appears on the right side of the thread is crushed, a chunk out of the top of the barrel, and a ding on the face of the barrel crown.
If my name were on it, I'd cut the barrel thread off, and turn, re thread, and crown the barrel, before attaching a muzzle device...especially a can.

Not a fan of thread files.

What happened? Why is the barrel device taken off? Was there ever a thread protector on it? Or something found along the side of the road.
If it's inexpensive, or moderately priced barrel just replace it.

 

[XLR308]

It appears on the right side of the thread is crushed, a chunk out of the top of the barrel, and a ding on the face of the barrel crown.
If my name were on it, I'd cut the barrel thread off, and turn, re thread, and crown the barrel, before attaching a muzzle device...especially a can.

Not a fan of thread files.

What happened? Why is the barrel device taken off? Was there ever a thread protector on it? Or something found along the side of the road.
If it's inexpensive, or moderately priced barrel just replace it.

I honestly understand your passion for perfection but your approach seems a bit like the saying " throwing the baby out with the bath water"
Thread files work perfectly fine for small clean up jobs like this.
And ince there is no damage to the the crown at the bore line were it matters it's kind of trivial at best considering a suppressor or muzzle brake will shoulder out at the rear of the thread against the step on the barrel.

 

[45-90]

I honestly understand your passion for perfection but your approach seems a bit like the saying " throwing the baby out with the bath water"
Thread files work perfectly fine for small clean up jobs like this.
And ince there is no damage to the the crown at the bore line were it matters it's kind of trivial at best considering a suppressor or muzzle brake will shoulder out at the rear of the thread against the step on the barrel.

Yes, being a professional machinist for 35 yrs, in nuclear, defense, areospace, and computer robotics, perfection is the name of the game.
I have a thread file, still in the package.
It was never used on a single part sold to world class customers, and never used in any rifle build.
You don't do that period.
Oh I tried it, once for it's intended purpose on a non important project, and abandoned it before long, and just cut the thread.

The real world...."I'm so particular."

You have what would be a scrap part, in this barrel, subject to quarantine in a locked cage, along with attached paperwork describing the problem, sign off on by the inspection department, and who is responsible, until disposal, of said part.

Not following these instructions one is subject for immediate discipline and dismissal. Falsifying the quality or feature of any part also subjects one to a 10yr prison sentence. Nuclear and DOD are super strict, one guy served 6 yrs in prison, for his efforts.
Try to send this barrel out to a customer would ruin the reputation of the company, and require immediate action, or loss of contracts forever.
I realize that parting off the damage threads, turning, and re threading this barrel is a very simple job for me, but its the correct way, easy to save, even if under legal length, could be dealt with.
But, since you do not possess the machine tools or skills, one can sub par things to gather and hope for the best.

If the barrel has some round count on it what's the problem with just replacing it. I replace worn barrels from shooting quite often...replacing barrels is part of shooting.
So IMO, I'm not throwing the baby out with the bath water.
The barrel is a replaceable consumable, when damaged it's easily replaced, if one can not properly repair it.
It looks like crap and no self respecting gunsmith or machinist would allow a part to look like that, plus if one can afford a suppressor, he can easily afford a new barrel, but a new barrel capable of accuracy, and a quality fit for his suppressor..win, win....
That's what I'd do if I were in his shoes...simple...and give ya an excuse to have a new barrel...I like new barrels.
But file away if ya want to....it ain't mine.
Never did say how the barrel came into its damaged condition.

 

[XLR308]

Yes, being a professional machinist for 35 yrs, in nuclear, defense, areospace, and computer robotics, perfection is the name of the game.
I have a thread file, still in the package.
It was never used on a single part sold to world class customers, and never used in any rifle build.
You don't do that period.
Oh I tried it, once for it's intended purpose on a non important project, and abandoned it before long, and just cut the thread.

The real world...."I'm so particular."

You have what would be a scrap part, in this barrel, subject to quarantine in a locked cage, along with attached paperwork describing the problem, sign off on by the inspection department, and who is responsible, until disposal, of said part.

Not following these instructions one is subject for immediate discipline and dismissal. Falsifying the quality or feature of any part also subjects one to a 10yr prison sentence. Nuclear and DOD are super strict, one guy served 6 yrs in prison, for his efforts.
Try to send this barrel out to a customer would ruin the reputation of the company, and require immediate action, or loss of contracts forever.
I realize that parting off the damage threads, turning, and re threading this barrel is a very simple job for me, but its the correct way, easy to save, even if under legal length, could be dealt with.
But, since you do not possess the machine tools or skills, one can sub par things to gather and hope for the best.

If the barrel has some round count on it what's the problem with just replacing it. I replace worn barrels from shooting quite often...replacing barrels is part of shooting.
So IMO, I'm not throwing the baby out with the bath water.
The barrel is a replaceable consumable, when damaged it's easily replaced, if one can not properly repair it.
It looks like crap and no self respecting gunsmith or machinist would allow a part to look like that, plus if one can afford a suppressor, he can easily afford a new barrel, but a new barrel capable of accuracy, and a quality fit for his suppressor..win, win....
That's what I'd do if I were in his shoes...simple...and give ya an excuse to have a new barrel...I like new barrels.
But file away if ya want to....it ain't mine.
Never did say how the barrel came into its damaged condition.

I hear you and understand your reasoning like I said before.
I know what it's like from past work we're every nut, bolt, screw, hydraulic fitting and hose, piece of steel, welds you name it has to have traceability with batch and heat number data with certificates from date and facility of manufacture so on and so on that all goes into a data book that is married to that piece of equipment.
But in reality its just a boogered up thread on a used barrel not a critical part on an F16 turbine engine or a space shuttle part.
I mentioned I had a muzzle thread on one my rifles that got goofed up a little similarly and thread filed it instead of risking seazing a brake up on it and it shoots in the .2 and .3's which is about as good as my old eyes and skills are capable of.
If he wants absolute perfection he wouldn't be asking about fixes here he would have just pulled the barrel and have it parted off and rethreaded or replace it.
So yeah I get it

 

[ma smith]

Yes, being a professional machinist for 35 yrs, in nuclear, defense, areospace, and computer robotics, perfection is the name of the game.

FYI....5/8-24 is an obscure spark plug thread...
Its only used on firearms AFAIK by historical accident.

Also, AFAIK....ICE engines don't turn into IEDs if you run a rethreader tap into a sparkplug hole,
otherwise you'd need ATF permission to but one of these $15 widgets from NAPA

 

[ma smith]

Here's a schematic of a field repair.

 

[ma smith]

Pleas note: this is not any kind of engineering advise,
this is just for informed-discussion purposes only.

FYI - spark plug helicoils = ±6 threads of engagement

 

[ma smith]

Here's an aerospace version...
View attachment 8507374

https://www.aircraft-tool.com/Detail?id=ATS486

I'm not an airplane tech so can't comment
if this is redneck or not in modern use.

Pretty sure based on google results
the car guys aren't scared tho...

Spark Plug Thread Inserts | STANLEY® Engineered Fastening

STANLEY offers Helicoil Spark Plug Thread Inserts to provide specific & unique benefits to high-temperature, high-performance spark plug applications. Learn more!

www.stanleyengineeredfastening.com

 

[XLR308]

Here's an aerospace version...

I'm not an airplane tech so can't comment
if this is redneck or not in modern use.

Pretty sure based on google results
the car guys aren't scared tho...

https://www.aircraft-tool.com/Detail?id=ATS486

Some people over think things to the degree of cranial paralysis due to lack of confidence or external guidance.
Thankfully I'm old enough to know what it's like to not have the internet and use intelligence and hands on experience to solve problems without 10000 hands up my ass and on my dick to experiment and figure things out on my own.
Don't get me wrong the internet is an extremely useful tool but if it went away tomorrow how many people would be completely lost and utterly useless ?
I am scared of the actual percentage that would be statistically useful in such a scenario.

 

[45-90]

Thread inserts, and heli- coils, can be part of industrial assembly, usually in aluminum parts, or plastics, soft materials, where high torque values required might strip the aluminum material threads, in new parts, as part of their designed . I have used them in aluminum fixtures for CNC machining, for years, bolting and unbolting repeatedly...and find them very useful.
Not sure it has any application here on a gun barrel, though.

 

[n2ishun]

Heli-coils and/or time-serts are for internal threads only.....and do you really think one would align well enough to not get baffle strikes on a can ?

Yea......uhh.....no.

 

[supercorndogs]

I reccomend them because I use them with great success.

Some even have a spike on the end for repairing internal threads, which I often do. Yes taps and die nuts work better, but in a pinch, and for a few dollars, they work fantastically.. for me.

I have never had trouble le using thread files either. I used my dad's set when I was little a few times. Then I bought a set for myself and used them in the shop many times over the years.

 

[lariat]

Yes, being a professional machinist for 35 yrs, in nuclear, defense, areospace, and computer robotics, perfection is the name of the game.
I have a thread file, still in the package.
It was never used on a single part sold to world class customers, and never used in any rifle build.
You don't do that period.
Oh I tried it, once for it's intended purpose on a non important project, and abandoned it before long, and just cut the thread.

The real world...."I'm so particular."

You have what would be a scrap part, in this barrel, subject to quarantine in a locked cage, along with attached paperwork describing the problem, sign off on by the inspection department, and who is responsible, until disposal, of said part.

Not following these instructions one is subject for immediate discipline and dismissal. Falsifying the quality or feature of any part also subjects one to a 10yr prison sentence. Nuclear and DOD are super strict, one guy served 6 yrs in prison, for his efforts.
Try to send this barrel out to a customer would ruin the reputation of the company, and require immediate action, or loss of contracts forever.
I realize that parting off the damage threads, turning, and re threading this barrel is a very simple job for me, but its the correct way, easy to save, even if under legal length, could be dealt with.
But, since you do not possess the machine tools or skills, one can sub par things to gather and hope for the best.

If the barrel has some round count on it what's the problem with just replacing it. I replace worn barrels from shooting quite often...replacing barrels is part of shooting.
So IMO, I'm not throwing the baby out with the bath water.
The barrel is a replaceable consumable, when damaged it's easily replaced, if one can not properly repair it.
It looks like crap and no self respecting gunsmith or machinist would allow a part to look like that, plus if one can afford a suppressor, he can easily afford a new barrel, but a new barrel capable of accuracy, and a quality fit for his suppressor..win, win....
That's what I'd do if I were in his shoes...simple...and give ya an excuse to have a new barrel...I like new barrels.
But file away if ya want to....it ain't mine.
Never did say how the barrel came into its damaged condition.

Perfection is absolutely not “the name of the game” in aerospace machining because there is no such thing, keeping within the designated tolerances is the standard. These threads are the same thing. There is no need to replace the barrel or put undue machining costs into a simple fix.

 

[45-90]

Perfection is absolutely not “the name of the game” in aerospace machining because there is no such thing, keeping within the designated tolerances is the standard. These threads are the same thing. There is no need to replace the barrel or put undue machining costs into a simple fix.

Perfection IS absolutely what one strives for...and end up with excellence in manufacturing.
Human, and machine don't have to be absolutly macular perfect to strive for perfection, and no one is talking about splitting atoms, or atom splitting tolerences...

Just having the threads, face, and shoulder be in tolerence with acceptable finish and appearance, would be nice...especially if you're gonna put a suppressor on it.
It costs me nothing to remachine the barrel, and could be done quickly.
Even for a gunsmith this is not a high doller endevor.
But it's not mine, so you can backyard mechanic it all ya want.
I've heard some ridiculous statements here...but no one has mentioned MacGyver and duct tape, cause I saw it on TV so it must be true...or maybe super glue, that works great too, or forget the threads and file a gentle taper and smack the muzzle device on with a hammer...bubble gum?

Speaking of areospace, Boeing could use a little more excellence in their manufacturing, as their planes fall apart in flight and some even crash...unacceptable IMO.

 

[db2000]

Perfection IS absolutely what one strives for...and end up with excellence in manufacturing.
Human, and machine don't have to be absolutly macular perfect to strive for perfection, and no one is talking about splitting atoms, or atom splitting tolerences...

Just having the threads, face, and shoulder be in tolerence with acceptable finish and appearance, would be nice...especially if you're gonna put a suppressor on it.
It costs me nothing to remachine the barrel, and could be done quickly.
Even for a gunsmith this is not a high doller endevor.
But it's not mine, so you can backyard mechanic it all ya want.
I've heard some ridiculous statements here...but no one has mentioned MacGyver and duct tape, cause I saw it on TV so it must be true...or maybe super glue, that works great too, or forget the threads and file a gentle taper and smack the muzzle device on with a hammer...bubble gum?

Speaking of areospace, Boeing could use a little more excellence in their manufacturing, as their planes fall apart in flight and some even crash...unacceptable IMO.

Amen

 

[lariat]

Perfection IS absolutely what one strives for...and end up with excellence in manufacturing.
Human, and machine don't have to be absolutly macular perfect to strive for perfection, and no one is talking about splitting atoms, or atom splitting tolerences...

Just having the threads, face, and shoulder be in tolerence with acceptable finish and appearance, would be nice...especially if you're gonna put a suppressor on it.
It costs me nothing to remachine the barrel, and could be done quickly.
Even for a gunsmith this is not a high doller endevor.
But it's not mine, so you can backyard mechanic it all ya want.
I've heard some ridiculous statements here...but no one has mentioned MacGyver and duct tape, cause I saw it on TV so it must be true...or maybe super glue, that works great too, or forget the threads and file a gentle taper and smack the muzzle device on with a hammer...bubble gum?

Speaking of areospace, Boeing could use a little more excellence in their manufacturing, as their planes fall apart in flight and some even crash...unacceptable IMO.

No. Perfection should be strived for but is ultimately unattainable. Any CMM will show that to be true. There is is huge difference in saying it is “the name of the game” and then subsequently saying it should be strived for. Why is it an issue? Because within the confines of this conversation it goes past machinist OCD and violates common sense advice for the average dude and could send him down a rabbit hole he doesn’t need to go through.

There isn’t anything wrong with the crown and the threads are easily repaired. There is no need to engage in hyperbole; no one has mentioned duct tape or other ridiculous things other than you. For the threads that need to be fixed the options that have been presented are easy and cheap and get him back in business.

 

[Cascade Hemi]

There's enough damage I would do what 45-90 is recommending.

 

[hkguns]

Well considering it doesn't look like those split dies are available anywhere, I personally would give the thread file a try.

 

[supercorndogs]

Remember any little bur, tag or left over shaving on stainless can easily roll into a ball and gall the barrel and whatever muzzle device into a 1 peice assembly. The guy makes a point about getting it fixed right. It's a 100 dollar bill, but it's cheaper than machining galled threads out of your can and then paying to have the barrel threaded.

 

[krw]

If any of yall hav ever worked maintnance at a Sawmill. Middle night, and you hav to get nut started. Don’t be a Puss. Pick up a thread file, straighten out threads, put dab grease on it, tighten nut and go to another job. Don’t make mountain out of a molehill!!

 

[Baron23]

some of this discussion reminded me of this...lol

 

[kthomas]

I dinged up the threads on one of my ar15 barrels, and used a thread chaser successfully to get a muzzle brake on.

I didn't have a big ding on the face of the barrel like yours, that would certainly require some careful filing to bring back down to allow a muzzle device to get to the threads.

 

[Mike Casselton]

View attachment 8505934
View attachment 8505935


Thread file is what you seek. The have a bunch of thread pitches on the one file. Cheap and work well for quick repair of dings.

That was my first thought

 

[45-90]

A tiny internal burr, or sliver of metal, may have been on the threads before removal of the barrel nut, around the indexing pin hole, or it just starts galling from pressure required to remove it, in this high torque area.
Once the small burr starts shaving metal, it keep going, adding more metal to interfere with removal...tearing the threads almost completely off. Lube and penetrating oil won't help much here, once the galling starts, and penetrating oil was already previously applied, but doesn't always work as planned.
This is real gun steel, and what a tiny internal burr or galling will do.
It only takes a tiny sliver of metal, or very small chip, left by any means, or thread galling to start this process.

Why Clean and lube threads, anti-seize application is recommended, by many manufacturers.
Even once threaded on does not mean ya wont have a problem with removal.
Like this old Rem 700 barrel torqued on the action for 50 yrs with rusty threads ...had to be mounted in the lathe and cut off the action, and still difficult to remove. Penetrating oil, didn't seem to penetrate here, but added more as the action was separated, from the barrel.
So matter how ya decide to attack the problem the clean thread, and lube/ anyi-seize should be strongly emphasized, during assembly.

 

[Cynical]

I have a barrel with a small ding right on the starting muzzle brake thread… I tried to start a muzzle brake on it to chase it or clean it up some, but there is not enough to get it started and me comfortably put any pressure on it… since I shoot suppressed, I need to clean it up and not affect the alignment of the can to the bore… Anyone have any thoughts or recommendations on a tool that would work? Or should I just file that one spot down?

View attachment 8505917

5/8-24? Rent this. https://4drentals.com/product/tool-rentals/rifle-tools/5-8x24-thread-chasing-die/

 

[atombomb]

5/8-24? Rent this. https://4drentals.com/product/tool-rentals/rifle-tools/5-8x24-thread-chasing-die/

it’s 3/4-24….. took a while, but used the swiss file for the threads and a flat file for the face and chamfer. Everything came out well and suppressor/brake alignment is perfect. thanks for that link, might come in handy….

 

[strikeeagle1]

5/8-24? Rent this.

Didn't know such a site existed. Thanks for that contribution.

 

[Rubicon Precision]

Using a standard triangle file would be my last choice. Too much chance for error in over-filing or getting it angled in an odd way. Either of the options above would work much better.

It doesn't matter other than looks. You're never going to change enough by filing one dented thread to affect anything. You could file that entire start thread off and it's not going to change a thing.

 

[LeftyJason]

It doesn't matter other than looks. You're never going to change enough by filing one dented thread to affect anything. You could file that entire start thread off and it's not going to change a thing.

You can even completely remove that entire partial thread and it won't affect anything. Just turns it into a higbee/ blunt start thread. Have done them by machine (thread cycle with a square groover) or by hand with an air grinder with a burr.

 

[n2ishun]

FYI....5/8-24 is an obscure spark plug thread...
Its only used on firearms AFAIK by historical accident.

Huh, who knew ?

Spark Plug Threads Sizes Table

Spark Plug Threads Sizes and Tapped Hole - The SAE Standard includes the following sizes: 7⁄8- inch nominal diameter with 18 threads per inch:

www.engineersedge.com

 

[ma smith]

5/8-24 is UNEF ("extra fine") thread spec, which is comparatively rare.

TR knowledge base | Thread geometry - Unified Extra Fine (UNEF)

Thread geometry for Unified Extra Fine (UNEF) threads.

www.trfastenings.com

A more comprehensive table of theads used in electronics (highlighted in yellow) includes it.

see line 35.

 

[Terry Cross]

A tiny internal burr, or sliver of metal, may have been on the threads before removal of the barrel nut, around the indexing pin hole, or it just starts galling from pressure required to remove it, in this high torque area.

That is not a tiny internal burr.
It is a damaged thread caused by banging the barrel extension indexing pin into place with a hammer.

There could be zero torque on the joint and this condition would still likely lead to galling and tearing metal once the damaged male threads are forced to rotate under perfectly good female threads.

Like this old Rem 700 barrel torqued on the action for 50 yrs with rusty threads ...had to be mounted in the lathe and cut off the action, and still difficult to remove. Penetrating oil, didn't seem to penetrate here, but added more as the action was separated, from the barrel.

As above, the issue was due to threads damaged by a goober not knowing how parts interact.
Your example with the Rem 700 results from the front screw for the scope base being too long but Johnny Gunsmith has his new MidWay gunsmithing tools knew exactly what torque to apply.

Since Johnny Gunsmith was reaching the desired torque by cramming the tip of the screw into the barrel threads instead of correctly letting the fastener head torque against the bottom of the base countersink, the barrel threads are smashed beyond recognition.

(Added awesomeness is that that front screw was probably doing exactly zero to secure the scope base since the head may have still been floating above the countersink without contact.)

So that thread mate was doomed to crash and burn as soon as it was forced to rotate the damaged male thread profile against it's opposing female profile.

Rusty threads had nothing to do with the hurdles facing removal.
Both examples are of male threads being trashed while the joint is mated making it difficult to avoid damage upon removal.
Neither of these examples seem to be relevant to the OP's question.



As stated by others above, the OP could take the damaged portion of thread totally out of play by relieving it below the existing base profile. No loss of accuracy, retention or alignment would occur.
The shoulder behind the threads appears to be intact and undamaged. That shoulder carries the vast majority of responsibility for correct alignment and retention.

Ditto for the ding on the face of the muzzle.
The ding is nowhere close enough to the actual crown to be concerned about any dimensional change at the bore/crown.

Any brake, suppressor or muzzle device is not going to know and could care less that previous material has been removed from the mating surfaces of its host.

 

[45-90]

That is not a tiny internal burr.
It is a damaged thread caused by banging the barrel extension indexing pin into place with a hammer.

There could be zero torque on the joint and this condition would still likely lead to galling and tearing metal once the damaged male threads are forced to rotate under perfectly good female threads.


As above, the issue was due to threads damaged by a goober not knowing how parts interact.
Your example with the Rem 700 results from the front screw for the scope base being too long but Johnny Gunsmith has his new MidWay gunsmithing tools knew exactly what torque to apply.

Since Johnny Gunsmith was reaching the desired torque by cramming the tip of the screw into the barrel threads instead of correctly letting the fastener head torque against the bottom of the base countersink, the barrel threads are smashed beyond recognition.

(Added awesomeness is that that front screw was probably doing exactly zero to secure the scope base since the head may have still been floating above the countersink without contact.)

So that thread mate was doomed to crash and burn as soon as it was forced to rotate the damaged male thread profile against it's opposing female profile.

Rusty threads had nothing to do with the hurdles facing removal.
Both examples are of male threads being trashed while the joint is mated making it difficult to avoid damage upon removal.
Neither of these examples seem to be relevant to the OP's question.



As stated by others above, the OP could take the damaged portion of thread totally out of play by relieving it below the existing base profile. No loss of accuracy, retention or alignment would occur.
The shoulder behind the threads appears to be intact and undamaged. That shoulder carries the vast majority of responsibility for correct alignment and retention.

Ditto for the ding on the face of the muzzle.
The ding is nowhere close enough to the actual crown to be concerned about any dimensional change at the bore/crown.

Any brake, suppressor or muzzle device is not going to know and could care less that previous material has been removed from the mating surfaces of its host.

If the difficulty in disassembly was caused by the same thing, as you say, basically a hammer on the indexing pin, possible it was factory assembled, but threads appeared fairly normal when looking into the hole, and a screw too deep on the scope base, damaging the thread...Then how come the outcome is not the same. No damage to the rusty thread on the Rem reciever or barrel and destroyed thread under the barrel indexing pin, which must have had a ding or chip in the thread.
I see them different...rust, and damage around the indexing pin...as the outcome is totally different.