muzzle brake thread size to caliber ratio

R

Rolandr

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What is the minimum size thread for a muzzle brake on a.30 barrel with a muzzle diameter .550 o.d. I have a Shrewd muzzle brake .625 o.d. with a 1/2 x 28 tpi and a Shrewd muzzle brake with a 7/16 x 28 tpi . and the 1/2 x 28 will be too thin at the threaded section and the 7/16 x 28 will leave the walls of the .30 caliber bore too thin. Is there a formula or rule as to the minimum diameter thread ratio to the caliber of the barrel?. T.I.A.
rolandr
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Rolandr said:
What is the minimum size thread for a muzzle brake on a.30 barrel with a muzzle diameter .550 o.d. I have a Shrewd muzzle brake .625 o.d. with a 1/2 x 28 tpi and a Shrewd muzzle brake with a 7/16 x 28 tpi . and the 1/2 x 28 will be too thin at the threaded section and the 7/16 x 28 will leave the walls of the .30 caliber bore too thin. Is there a formula or rule as to the minimum diameter thread ratio to the caliber of the barrel?. T.I.A.
rolandr
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The 1/2 x 28 will work. Thread the barrel and try the brake several times as you are getting close to finishing... you will want it to be as snug as you can get it, and yet not binding when installed with your fingers... perhaps do a test piece before you do the barrel...
 
I'm going to assume there is a counter bore in the break. measure the diameter of that. As long as you can get good contact between the shoulders of the barrel and break the 1/2-28 will work.

Dave
 
muzzle break threads

Dave, there is a counterbore on the brake but if I want to blend the brake with the barrel muzzle it will leave a very thin surface to mate against the barrel. The barrel is .550 and the o.d. at the brake counterbore is .625, that will leave a .037 thick wall on the brake, do you think that is enough to tighten up properly?. Thanks
rolandr
 
with the barrel o.d being that small, i would tapper the brake to the barrel.
 
rolandr

You'll have a threaded shank diameter about .495" You have a barrel dia. of .550" minus the diameter of the counter bore. Divide that by two and you have the contact area on the shoulder. It doesn't take much to keep one tight. Is the wall thickness there enough to handle the pressure? probably so. I wouldn't taper the rear of the break too much. Just break the edge or taper the last .375".

Dave
 
I have done probably a hundred or more of these... sometimes you can not make the taper right down to barrel diameter... sometimes the barrel is not concentric... they still look good turned close and rounded slightly... with Never Seize high pressure lubricant on the threads and tightened up snugly with a short punch though a hole, it will work fine... Brakes do not need to be installed with a lot of torque.. just snug with a short punch and the butt stock between your feet...

The counter bore is usually about .505 or so... you will have a shoulder of about 20 thou per side.. it will work if your work is accurate.
 
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muzzle brake

Thanks a bunch guys, that will get me going on this project. I just didn't want to play with the safety part of it.
Rolandr
 
There's not really a safety issue. I've had more than one come back with the front part of the brake gone. Even had one I forgot to bore the hole out oversize that was swaging 30 cal bullets through a 7MM hole in the end of the break. Ooops. You name it and I've probably done it somehwere along the line.

Dave
 
The guy called, he's a good friend so that helped. and said " Why are my bullets hitting the dirt at 75 yds.?"

Then a light came on. You idiot, you forgot to bore the break out. Oh well 'bring it back and I'll make another one". Probably won't be the last time.

Dave
 
Dave

Dave Tooley said:
The guy called, he's a good friend so that helped. and said " Why are my bullets hitting the dirt at 75 yds.?"

Then a light came on. You idiot, you forgot to bore the break out. Oh well 'bring it back and I'll make another one". Probably won't be the last time.

Dave
Click to expand...
,,,,,,,,,,,,,,,,,,,,

Well, these happen,,,,,, sometimes. I'll bet that after you've reliazed what you've done or rather forgot to do, "the damn phone" didn't ring for a long while.

Shoot well
Peter
 
Here are a couple of pictures of a .550" barrel (HS Precision 300 short mag).

This brake is .700 in diameter. I don't like them any smaller although it could be turned down to match the barrel contour... I think the larger diameter works a bit better.

Rather than try and take it right down to the barrel contour I prefer to stay a few thou larger and finish with a small radius.

thin%20barrel%20brake%201.jpg

thin%20barrel%20brake%202.jpg


Blasted for a dull finish.
thin%20barrel%20matte%20brake.jpg
 
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Question....

What is the minimum thickness between the bore I.D and the and the O.D of the shank for the muzzle brake? Example .830 barrel dia., .224 cal., 1/2 shank for muzzle brake leaves appx. .138 wall thickness (minus thread depth). Is this safe? Will accuracy suffer? Should a larger shank be turned?

Thanks in advance,
JKM
 
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Troy Newlon of Newlon Precision has a book out on muzzle brake fitting and design. He answers pretty much any question you might have on designing, building and fitting muzzle brakes. The section on threading is worth the price alone and applies to all threading jobs you might do. He recommends .050" per side (.100" total) on the brake shoulder to barrel. On a 1/2x28 thread he recommends a minimum .600" barrel diameter so an .830 barrel with a 1/2 thread would be ok by his recommendations.
 
Thanks for the reply......

But, I am wondering how much wall thickness is needed on the barrel over the bore diameter. I had a muzzle brake installed on a 338 RUM with a .670 dia. barrel, the shank/tenon for the brake is 9/16" so .670-.5625=.1075, that seems a little thin to me. I am now capable of doing my own brakes now and would like to know much can be turned off the barrel diameter of various calibers without becoming unsafe or affecting accuracy. Is there a standard barrel wall thickness at the muzzle that needs to be maintained or does it vary by caliber or cartridge?

P.S. I looked up that book looks quite interesting, I think I'll take your advice and order it.

Thanks,
JKM
 
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Oops, sorry I missed your actual question. I don't think the minimum bore to thread wall thickness was addressed in the book. I'll look through it again and see if it does. If not, a call or e-mail to Troy would give an answer as to what his opinion would be. He is very helpful with questions when you can get him.

The major dia of 9/16 thread is .5625-.338 bore=.2245 total wall thickness. .1123 per side. I don't know if that is good or bad. You certainly wouldn't want a thread relief and would want a radius on the barrel shoulder. A shoulder on the barrel matching a counter bore at the back of the brake would probably be helpful too. On the index bushing thread Stiller did some strength calcs with stacked tenon to bushing to action strengths which should apply here. If the thread fit was say a tight class 3 and you used a finer pitch say 32 TPI I would think it would be plenty strong enough but would the pressure be high enough to expand the bore/brake at the muzzle? Probably no more than the original barrel. A common threaded muzzle is an AR15 with 1/2x28 thread. .5 thread-.224 bore =.277 wall. .1385 per side. .0262 per side difference from AR to your .338 a fair amount. Looking back to the beginning of this thread with the barrel dia of .550 and .308 bore which had .121 per side wall thickness many said this was safe. Maybe someone else will have an opinion on whether your situation is good or bad.
 
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Thanks again..........

WSnyder said:
Oops, sorry I missed your actual question. I don't think the minimum bore to thread wall thickness was addressed in the book. I'll look through it again and see if it does. If not, a call or e-mail to Troy would give an answer as to what his opinion would be. He is very helpful with questions when you can get him.

The major dia of 9/16 thread is .5625-.338 bore=.2245 total wall thickness. .1123 per side. I don't know if that is good or bad. You certainly wouldn't want a thread relief and would want a radius on the barrel shoulder. A shoulder on the barrel matching a counter bore at the back of the brake would probably be helpful too. On the index bushing thread Stiller did some strength calcs with stacked tenon to bushing to action strengths which should apply here. If the thread fit was say a tight class 3 and you used a finer pitch say 32 TPI I would think it would be plenty strong enough but would the pressure be high enough to expand the bore/brake at the muzzle? Probably no more than the original barrel. A common threaded muzzle is an AR15 with 1/2x28 thread. .5 thread-.224 bore =.277 wall. .1385 per side. .0262 per side difference from AR to your .338 a fair amount. Looking back to the beginning of this thread with the barrel dia of .550 and .308 bore which had .121 per side wall thickness many said this was safe. Maybe someone else will have an opinion on whether your situation is good or bad.
Click to expand...

I can see now that my math was a little off, thanks for clearing that up(newby mistake). I may have to drop Troy a note to get his opinion, my338 seems to shoot alright still, but if it is indeed to thin, I don't want to make that mistake myself going forward with my own projects. I also don't want to sacrifice accuracy or most importantly...safety!

Thanks Again,
JKM
 
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