3/4-24 muzzle brake threads.

[DHuffman]

It might not get close enough to the shoulder and the brake won’t thread on all the way

At that point you could turn the die over so the finish side of the die goes to the shoulder instead of the tapered starting side.

The split die could probably run that way from the start.

 

[Tucker65]

Ideally it should go back in the lathe to cut them to the correct size.

Depending on how snug the threads are it's possible you could put some lapping compound on the threads and work the brake or thread protector back and forth to get them to fit. If it's stainless on stainless you have to be very careful about galling the threads.

 

[iam1964]

Thanks for all the great advice guys.

 

[JMA]

If you can't use wires and a mic, you aren't a real machinist!
In all seriousness, I remember my instructor in level 3 of my machining apprenticeship going on a bit of a tirade about the hidden pitfalls and potential inaccuracies of thread mics.
I've avoided them ever since, and after using the wires for so long, I don't even find them a pain.

Most of my career I worked in machine shops and I never saw threads checked useing the 3 wire meathod. We always used thread mics or ring gauges. Occasionally the mateing part was used, if a mathaince job
a nut. Much of the work was for the airospace industry where tolerances and fits had to be held.
I tried using 3 wires at home once what a pia swore next time I bite the bullet and buy a thread mic for at home.

Not saying any thing is wrong with 3 wire meathod but there are easier ways.

 

[iam1964]

Guys, just an update. My buddy ran a die down the thread and it now fits perfectly.

Thanks again for the help.