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

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

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

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 zimmer

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

Scientists are all over the show nowadays, safer to stick with Engineers......

Yeh, they were only students doing a degree in Mech Eng at Canterbury Uni in the late 70s. Obviously the curriculum was all to hell..