Bore diameter changes when turning down muzzle end?

[TAJ45]

I believe I read that Bill Calfee said a tenth growth. Dont remember any more than that - too long ago.

 

[Cauthon]

As you all know I work for a button rifle barrel manufacturer that's been around for at least 70 years if there was any merit to the myths of bores opening up even a tenth or so we would be getting hold of the steel mill asking questions we rely on a heat of steel to shrink the same that's why we buy a whole heat when we purchased steel.

If you are OK with commenting further, it would be interesting to know if you can measure a difference in the outside diameter of a barrel, before and after (or during) button rifling. And if you can see a difference in that effect depending on the contour of the barrel - especially when making a barrel liner, a lot smaller o d than a normal barrel. Thanks.

 

[gunsandgunsmithing]

If you are OK with commenting further, it would be interesting to know if you can measure a difference in the outside diameter of a barrel, before and after (or during) button rifling. And if you can see a difference in that effect depending on the contour of the barrel - especially when making a barrel liner, a lot smaller o d than a normal barrel. Thanks.

It'll have to be someone else. Stan is no longer with us. He is missed.

 

[jackieschmidt]

this isn't that hard just check before and after with deltronic pins....

^^^^^^^
If I can’t pick up the difference with a Deltronic Pin, I seriously doubt a bullet will notice it.

 

[Greg Y]

I'd be more worried about someone hambfisting the brake on and pinching a spot. That's at least a legitimate potential.

 

[skeeljc]

This thread isn't worth making popcorn for.

 

[Edd]

Barrel End Threading — Bigger Diameter is Better « Daily Bulletin

Our friend Robert Whitley of ARX Enterprises LLC has learned, through careful measurement and testing, that some barrels threaded 5/8 x 24 TPI at the muzzle may not deliver optimal accuracy.

bulletin.accurateshooter.com

 

[gunsandgunsmithing]

This thread isn't worth making popcorn for.

I disagree. What don't you understand or did you know this already? Kinda an open ended statement. There's a lot of misunderstanding about bolt thrust and the reasons for AR15 lugs shearing off. Happy to try and help if I can, though.

 

[tobnpr]

There's a lot of misunderstanding about bolt thrust

I wasn't going to get involved in this necro thread, but...
What does bell-mouth at the muzzle have to do with bolt thrust?

 

[INTJ]

I used to worry about the bell-mouth when turning down muzzles. It seems like every barrel that comes through the shop winds up being threaded.

I quit worrying about it when the guys at Defensive Edge said they had threaded .338 bore muzzles to 1/2-28 and had no accuracy issues. And those guys know what they are doing and have been doing it for a long time......

Now for my own personal rifles, I will keep the threads as large as I can on the very few that I do thread. My 1K BR heavy gun is threaded 1"x 32 and it shoots very well. However, that is a BR rifle where little stuff matters.

With almost any other shooting discipline, and ESPECIALLY for hunting rifles--short, mid, and long range; threading the muzzle thinner than we like doesn't really seem to make any difference in most cases.

 

[Carl S]

Turned,threaded and shortened lots of them for suppressors and brakes..only thing noticeable was an improvement in accuracy on the target.

 

[gunsandgunsmithing]

I wasn't going to get involved in this necro thread, but...
What does bell-mouth at the muzzle have to do with bolt thrust?

Huh? Different thread maybe. Idk.

 

[akajun]

I’d read/ been told years ago one of the military teams found when turning the end of the barrel down for the flash hider on NM m14s that unless they took small cuts and used lots of coolant that they were bell mouthing some barrels and it was showing up at 600/1000 yds
My personal experience with machining in general is you can generate enough heat to induce/ release stress and distort a part
Do something like get it hot then drop some cold cutting oil on one spot and you can cause problems, especially on smaller parts
When I do muzzles, threading, etc I use light cuts and a mist cooler so the barrel never gets slightly warm. I’ve never had a problem

 

[V35]

I always go as big as possible. I have seen one barrel open up by.001”, measured before and after with pins. It was a hammer forged barrel. I have done several just like it prior to and after that never moved.

 

[urbanrifleman]

myths

 

[DickE]

I believe John Whidden has an article here somewhere, where he did a test of muzzle threading. 1/2x28 tpi opened the muzzle, 5/8x24 tpi did not.

 

[DShortt]

This is an old thread but apparently there is still interest.
I can tell you I've seen several .30 cal factory barrels from a manufacturer that is widely considered to be among the best for budget factory rifle accuracy where the chamber end of the barrels were .0015" to .002" smaller than the muzzle end.
Obviously if someone were to thread such a ballel and measured it afterward then a pre-existing condition might be observed after the fact.

Edit to add - I think sporter weight button rifled factory barrels should be viewed with a skeptical eye by those interested in accuracy. Yes, they will function just fine for hunter's at close to moderate ranges. And to expect more than that at their price is probably not reasonable.

 

[Limafoxtrot2]

I have experienced muzzle growth on button rifled blanks on at least three occasions that I aware of. The muzzle tenon diameter on these barrels was .625" and the unfortunate fact is that these particular barrels would not consistently group during test firing. I used pilots on a range rod to closely gauge them and then I slugged the bores and felt the looseness at the muzzle. My solution was to counterbore the muzzle face .125" behind the shoulder of the muzzle tenon. After the counterbore the rifles were shot again and they then grouped as I expected them too.

 

[tobnpr]

Edit to add - I think sporter weight button rifled factory barrels should be viewed with a skeptical eye by those interested in accuracy. Yes, they will function just fine for hunter's at close to moderate ranges. And to expect more than that at their price is probably not reasonable.

Respectfully disagree.
I've built many hunting rifles for customers with sporter contour barrels that are every bit as accurate as heavy contours- and button rifled barrels can be just as accurate as cut rifled, but I concur they are less consistent.

Barrel contour has zero to do with the accuracy potential of a barrel. The problem is that some shooters lack the understanding that sporter barrels lack the mass needed to use for target shooting; they heat up rapidly, lack the rigidity of heavier contours and start stringing shots. Used as intended- a cold bore with at most a few follow up shots- a sporter contour barrel should be every bit as a varmint or bull. Additionally, range is irrelevant. The bullet doesn't know whether it's launched from a #2 or a #7 contour- length affects velocity, not contour.

 

[DShortt]

Respectfully disagree.
I've built many hunting rifles for customers with sporter contour barrels that are every bit as accurate as heavy contours- and button rifled barrels can be just as accurate as cut rifled, but I concur they are less consistent.

Barrel contour has zero to do with the accuracy potential of a barrel. The problem is that some shooters lack the understanding that sporter barrels lack the mass needed to use for target shooting; they heat up rapidly, lack the rigidity of heavier contours and start stringing shots. Used as intended- a cold bore with at most a few follow up shots- a sporter contour barrel should be every bit as a varmint or bull. Additionally, range is irrelevant. The bullet doesn't know whether it's launched from a #2 or a #7 contour- length affects velocity, not contour.

I respect your opinion but I also disagree. When I stated that I had slugged numerous barrels and found that the bore diameter was larger at the muzzle than at the chamber I wasn't kidding. Such barrels are not capable of consistent accuracy.

Now, having said that if the shooter and the rest of the system can't see the difference then it doesn't matter in that particular case. I'm not speaking to rapid fire and barrel deflection due to heat. These were cold bore soft lead slugs inserted from both ends of the bore and measured. Indisputable results particularly when I saw it numerous times.

A one MOA barrel will bring home the bacon at close to medium range more often than not. That was my range reference and the reason I specifically mentioned hunting rifles. If you test the same barrels on paper then you will in fact see the difference. How do I know? Because I have tested those barrels. To say that it's reasonable to enter an accuracy contest with this grade of barrel and expect to be highly competitive is simply poor advice.

We can disagree. That's fine. I stand by my statements and know they are true because I've done the testing.