Muzzle threading diameter and accuracy

[TAJ45]

Seeing as we are into metallurgicalities, , has anyone cryo'd a bbl after stress relieving? It seems the big deal was to but our sine vice parts in our deep freeze for several days to retard any "shifting, growing" etc. Probably did the final grind afterwards.

 

[Old Navy]

I've noticed this on "less expensive" barrels. I can slide a pin in, until the shoulder.


FWIW: I use 3/4-24 - that seems to be a standard for big bore stuff. Don't know what uses 28tpi

I had my smith install a Holland Big Brake years ago. That is a 3/X28. I wanted to use it on several guns, so I just stayed with it. My Thunderbeast is the same also.

 

[gunsandgunsmithing]

Seeing as we are into metallurgicalities, , has anyone cryo'd a bbl after stress relieving? It seems the big deal was to but our sine vice parts in our deep freeze for several days to retard any "shifting, growing" etc. Probably did the final grind afterwards.

Working with a bbl maker on just such a test. It may be a little while but, yes, in the works.
Because cryo can slightly change bore dimensions(it gets tighter), the plan is to test before and after, sending the same bbl back to the maker to be lapped as closely as humanly possible, to the same dimensions as pre-cryo.

I have my suspicions as to what to expect but testing is how we know stuff like this. I suspect the results will be demonstrable but we'll see. Either way, I'm not sure it can be tested more similarly....pre vs post.

 

[Alex Wheeler]

Krieger used to in house cryo all their barrels. They stopped doing this quite a few years ago. I used to order a lot of barrels from them and got to know a couple of the guys in the back, one was the foreman. Guys that know whats going on and guys that had always been straight with me. I asked why they stopped doing it and they said it did nothing. Barrels didnt machine better, didnt drill straighter, ext. But I know some that swear by it. I worry more about the steal being properly stress relieved. Are most barrels really 100% stress free, I doubt it.

 

[RubiconJoey]

I don't have the means to actually test it, but for the sake of "science" I would love to see the same gauge pin test done on barrels before and after threading. If the logic is to be followed a barrel should be "tight" before threading and "open up" after threading.

 

[L.Sherm]

I don't have the means to actually test it, but for the sake of "science" I would love to see the same gauge pin test done on barrels before and after threading. If the logic is to be followed a barrel should be "tight" before threading and "open up" after threading.

Does the guage pin matter or the target?

 

[L.Sherm]

Are most barrels really 100% stress free, I doubt it.

I agree 100% Alex.
Do some have less than others, absolutely. The process is what matters if you start with good steel.

 

[urbanrifleman]

I worry more about the steel being properly stress relieved.

There you have it.

 

[RubiconJoey]

Does the guage pin matter or the target?

Putting rounds on target introduces a lot more variables, that as well all know are very difficult to control. This simple test eliminates those variables. That's not to say that this test doesn't have it own variables. Barrel material, the cutting tool, tool pressure, material removal rate, lubricant, even the temperature of the barrel when its gauged matters when we're talking about dimensions this small. It's about understanding what's physically happening. Does the barrel actually open up as a result of threading? If so, at what diameter does it open up?

However, as @Erik Cortina says, believe the target. The barrel may open up, but does it actually matter? For completeness I would love to see groups shot pre and post threading. I would however be very critical of the results of that test. If you see a difference you have to question what caused the difference. Was the difference due to the ammo, shooter, environment, a change in barrel harmonics due to the change in weight at the muzzle, the bore opening up or something you didn't even realize was a variable? The difference may be so small that it could get lost in the noise of all of those variables but, it doesn't necessarily mean that it doesn't make a difference.

As you can see it can be very difficult to attribute a change on target (if there is one) to the barrel opening up. However, it's impossible to attribute it to the barrel opening up if you don't actually know if the barrel opened up.

 

[boltfluter]

Straight from the machinist handbook - any outside turning, threading, polishing, bead blasting, etc, etc will reduce stress. That is, if there is any stress to begin with. We are living in the age of some of the very best quality barrels to ever be produced. After speaking with several friends that make barrels, the hardest part in today's world is getting good inclusion free steel to begin with. Many source their steel from Germany. Who knew!

 

[majohnson]

You can have the barrel air gaged. See if they will do with and without the brake.

 

[Will Henry]

I do believe stress relief is one of the more important factors in barrel manufacture. I'm sure most start with stress relieved steel to start with. The question then becomes, was the stress relief really done as required? Or, was stress induced during transport or handling?
Assuming the material is stress free, machining should not induce any stress, unless the operation is one of material displacement rather than material removal. If, when material is removed, the piece warps or changes dimension (apart from the material removal, of course), then there was stress present in the material. If there is no movement, there was no stress, or at least none sufficient to be noticeable.
I agree that the steel quality is the biggest hurdle for barrelmakers. Given good steel, the rest, including stress relief, is up to them. WH