3/4-24 muzzle brake threads.

[iam1964]

A friend of mine recently bought a barrel and had it threaded for a 3/4-24 muzzle brake. He has now tried it with two different muzzle brake and none of them fit. They start to go on but eventually stop and will go no further. The strange thing is that a 3/4-24 thread protector will screw on recently.

The muzzle brake are both from reputable companies as is the barrel. I have attached a couple of photos to show how far it will screw on.

Does anyone have any idea what may be going on?

Thanks.

 

[DHuffman]

The threads on the barrel are oversize to the brake but not the thread protector which has looser threads.

I've threaded a few of my own recently and they are like that until you take that last .001" pass to get to size.

Threads in the brakes are obviously smaller/tighter than the protector.

When threading a barrel it starts just like you describe until you finally get to clearance.

 

[iam1964]

The threads on the barrel are oversize to the brake but not the thread protector which has looser threads.

I've threaded a few of my own recently and they are like that until you take that last .001" pass to get to size.

Threads in the brakes are obviously smaller/tighter than the protector.

When threading a barrel it starts just like you describe until you finally get to clearance.

Thanks.

Is there an easy fix for this or does it have to go back to the gunsmith.

Is it possible to just buy a 3/4-24 thread die and run it down the barrel threads?

 

[Walt Krafft]

Thread protectors all have oversize threads in my experience. I have ring gages for the common sizes. Even then I prefer to have the brake in hand when I thread a barrel. Easier to go smaller when set up than trying to rework it.

 

[DHuffman]

Hard to see in those pics but the barrel threads still look pretty "fat"

 

[DHuffman]

I'm sure someone better on a lathe than I could reindicate the barrel and pick the thread back up but I'd probably cut it off and start over with the brake in hand.

 

[iam1964]

I'm sure someone better on a lathe than I could reindicate the barrel and pick the thread back up but I'd probably cut it off and start over with the brake in hand.

Do you think it would be possible to use a hand die without a lathe?

 

[DHuffman]

Do you think it would be possible to use a hand die without a lathe?

Theoretically I guess but I don't think I would.

 

[DHuffman]

I'd let the person that did the threads correct them.

 

[Jonnyofalltrades]

This is very common for gunsmiths that aren't machinists. If a guy is using a female threaded component to check the fit of his threads it's a total gamble whether or not a different component with the same thread is going to fit.
The correct way is to measure with a micrometer over wires, or with a thread micrometer, or with go/nogo ring gauges.
Threads are standardized, there is no point in hand-fitting(unless you don't know how to read a mic).

 

[LVLAaron]

I use machinist calculator, and hit the middle of a 2A/B spec unless there's some reason not to.

machinists

Unrelated.... A real machinist can use 3 pin gauges to measure a hole

edit: ^ That's not me.

 

[paperpuncher]

Do you think it would be possible to use a hand die without a lathe?

I’d put it back in the lathe and recut the thread but I don’t see any reason you couldn’t use a die. The thread is established already the die is going to follow it. I would get an adjustable split die and creep up on proper fit. A quick search shows dies available

 

[iam1964]

I’d put it back in the lathe and recut the thread but I don’t see any reason you couldn’t use a die. The thread is established already the die is going to follow it. I would get an adjustable split die and creep up on proper fit. A quick search shows dies available

That is what I was thinking. It may be worth trying. What is the worst thing that could happen?

 

[DHuffman]

I use machinist calculator, and hit the middle of a 2A/B spec unless there's some reason not to.


Unrelated.... A real machinist can use 3 pin gauges to measure a hole

edit: ^ That's not me.

I've threaded 4 of my own barrels for brakes so far and chambered one barrel as well as set back 2 others.

I'm officially at the "get close then check every pass for fit" stage at this point.

 

[paperpuncher]

That is what I was thinking. It may be worth trying. What is the worst thing that could happen?

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

 

[JMA]

I use machinist calculator, and hit the middle of a 2A/B spec unless there's some reason not to.


Unrelated.... A real machinist can use 3 pin gauges to measure a hole

edit: ^ That's not me.

a real machinist uses thread mics

 

[hogpatrol]

I see it's a self timer so have to ask, is he following the instructions? There might be something else going on here besides thread fitment.

Edit: That install doesn't match up with this video.

 

[iam1964]

I see it's a self timer so have to ask, is he following the instructions? There might be something else going on here besides thread fitment.

Edit: That install doesn't match up with this video.

He is doing it correctly. He has that brake on another two rifles with no issues.

 

[Jonnyofalltrades]

a real machinist uses thread mics

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.

 

[STS]

An adjustable die will take care of the issue in about 2 minutes and do a excellent job doing it. Start loose and continue to decrease the size until that pesky last .001 comes off. Available in 3/4 X 24.