Thread: Machinist/Gunsmiths Muzzle Threading Query

Have two rifles with threaded Muzzles and was having a look and thought neither looks like what I thought I remembered my old threaded rifles looked like.

One doesn't seem to have a square shoulder and one doesn't seem to have a relief cut.

Is this just different ways to suck eggs or something to have looked at?

I don't know much about this side of things so thought I'd ask the NZHS forum.

Don't know if it matters but ones for a brake and one a suppressor.

Cheers,
Cam

To clarify this is a query not a criticism as I have not real experience. The one with the relief cut I think just looks like it's not a square shoulder as the relief is a radius.

Relief Cut 1/2x28


No Relief Cut 5/8x24

As long as your appropriate attachments fit properly it shouldn't be an issue.
The radius relief cut if anything is mechanically superior to a square one as there will be no sharp corners but in this case it's not a problem.
Having no radius is fine as long as you can get the thread hard up against the shoulder. To err on the side of caution I would probably stop just before I got to the shoulder and do a relief cut.
But it does depend on the lathe and tradesman

Thanks for the responses. Wasn't sure whether the relief functioned to allow ensure the suppressor could but against the shoulder without the threads binding. Threads seem good nice and snug and would expect them to be concentric to the bore.

As for the relief radius that makes sense as it removes a stress point I guess what I meant is it kind of looked like the radius ended above the major thread pitch.

How would you tell whether the suppressor buts up against the shoulder on an over barrel style?

Will see how they both shoot these coming few weeks.

How would you tell whether the suppressor buts up against the shoulder on an over barrel style?

What kind of suppressor? If dpt, take off the barrel bush and see if it butts up hard to end of thread? Otherwise ive no idea

As posted it is a fine line on some lathes to get the last cut consistently up against the shoulder without cutting into it. This can mean you cant screw something hard up against the shoulder unless there is a big enough chamfered on the end.
I was a fan of making a relief to make this go away. Down to about the root level of the thread but do it before I started threading.
Your one looks like it was done after to mitigate what i have mentioned

Originally Posted by mimms2

Out with your engineers blue. (Or a vivid)...Colour in the shoulder and thread on and off a few times. See if it's all rubbed off (or, 80%+ contact)... or leaning to one side

Mint will give that a go.

Originally Posted by keengunNic

How would you tell whether the suppressor buts up against the shoulder on an over barrel style?

What kind of suppressor? If dpt, take off the barrel bush and see if it butts up hard to end of thread? Otherwise ive no idea

It's a dpt but you definitely can't see the shoulder through the can even with baffles removed as that was my first thought

Originally Posted by mimms2

From an engineering perspective a thread should never go to a shoulder without relief as it creates a stress riser and is less likely to load the pitch correctly, and so let the thread do it's job.
= always relief.

Shoulder should be square to the bore. This may or may not coincide with the exterior of the barrel.

This is vaguely what I thought I'd had heard and why I asked the question.

Originally Posted by mimms2

From an engineering perspective a thread should never go to a shoulder without relief as it creates a stress riser ..

I would have thought a square-corner relief cut would be an equal stress raiser

Originally Posted by Mauser308

Humph. I will ask my autocorrect to please get it right next time... Humblest apolagiez ona behelf of me phun nd itz poah spellinz...

If if we're going to split hairs the "science" is Finite Element Analysis usually abbreviated to FEA.

As a machinist and gunsmith Im with Mimms2 on this. Always have a relief cut and a shoulder.

I normally get stuff like this in my shop when the owner or new owner wants to fit a new/another muzzle device and cannot get it to thread on all the way up to the shoulder. I always remind myself to cut the thread not for a specific attachment.

I've had barrels in my shop where the thread ends with a 45 or 60° shoulder. The silencer manufacturer was of the opinion that a taper is supposed to assist with alignment....which it did'nt - a flat shoulder to bottom out against would have been better.

Originally Posted by Jaco Goosen

As a machinist and gunsmith Im with Mimms2 on this. Always have a relief cut and a shoulder.

I normally get stuff like this in my shop when the owner or new owner wants to fit a new/another muzzle device and cannot get it to thread on all the way up to the shoulder. I always remind myself to cut the thread not for a specific attachment.

I've had barrels in my shop where the thread ends with a 45 or 60° shoulder. The silencer manufacturer was of the opinion that a taper is supposed to assist with alignment....which it did'nt - a flat shoulder to bottom out against would have been better.

Would you ask to have a relief cut if it was returned like pictured that's a freshly cut thread the other wasn't done during my ownership.

If it is currently shooting well don't bother, ask for a relief cut when you have the crowns cleaned up/recut at some stage.

If you are considering changing a muzzle attachment or if you have any doubts, ask for a relief cut.

Originally Posted by mimms2

That was @ the other fullah who put the word "raiser" in bold...

and it looks like "riser" is a more modern US spelling abortionation. I had three mech eng flatmates at uni and heard the term often enough.

https://www.sciencedirect.com/topics.../stress-raiser