Muzzle brake clearances

woodchopper

woodchopper

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So I've been experimenting with building muzzle brakes and how tight I can cut the clearances to.

I have always assumed that tighter is better, but there is a limit to how accurate you can be.

over the weekend I tried a 243 with the brake drilled out to 0.250" so that's only 0.007" or average 0.0035"

it was too tight of tolerance and tagged the brake.

So I got to thinking how much clearance is there on a commercial brake, I measured one and on a 7mm (.284) the brake was .305" so 0.021" or average 0.0105" so a lot more then what I was thinking.

what is the consensus on how much clearance is needed ?
 
I was pretty sure that Ultimate Reloader and MDT did some brake testing "science"
Precision and concentricity are of significant import as well.
Upshot being that tighter tolerances aren't much worth the risk.
 
Its been my experience sure you can absolutely strip the bullet of its airflow with super tight diameters if everything is very concentric.
But always believed the best your gonna get for consistency includes an even, air buffer as the bullet passes though.

Which is .020"+
 
Suppressors are typically about 0.05" clearance from what I've seen, some of them even require the use of an alignment rod to get the can concentric.

So the answer is likely somewhere between 0 and 0.05".

Aside from the risk of baffle/brake strike, tightening your clearances would likely risk throwing off your POI due to the unpredictability of the increased gas-stripping from the closer spaced brake baffles.
 
woodchopper said:
what is the consensus on how much clearance is needed ?
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Like digitalblue says, suppressors are typically around 0.050" clearance on diameter. One thing not mentioned here is that the threads on the barrel may not be perfectly concentric and colinear with the bore. It's common enough that you always need to check to be sure a can is straight with the bore when you first install it on a firearm. The tighter the clearance, the more likely this becomes a problem.

Beeron said:
That's what I remember.
You don't get much benefit from very tight tolerances over more general ones.
Like a 308 brake is perfectly ok for a 6.5 CDm for example.
Click to expand...
yomamma is making a joke at your expense. Look at post #3 to see why.


Mark
 
mmattockx said:
Like digitalblue says, suppressors are typically around 0.050" clearance on diameter. One thing not mentioned here is that the threads on the barrel may not be perfectly concentric and colinear with the bore. It's common enough that you always need to check to be sure a can is straight with the bore when you first install it on a firearm. The tighter the clearance, the more likely this becomes a problem.


yomamma is making a joke at your expense. Look at post #3 to see why.


Mark
Click to expand...
ya,

he's probably never typed anything while someone else is typing something.
 
When I fit a brake, the barrel is dialed in on the bore and the threads are cut. The brake, which is undersized, is then threaded onto the barrel, and bored to finished diameter. Set up this way, the bore of the barrel and the bore of the brake are absolutely coaxial, and close tolerances can be held without risk of the bullet striking the brake.
Commercial finished brakes, intended to be installed on any barrel with matching threads, must be bored oversized.
 
20thou is pretty tight IMHO, but doable by a talented Smith, requires some serious alignment and boring concentric to the bore.
Commercial brakes have to deal with factory rifles with possibly off center bores, so they generally go on the larger side, 40-50 thou sort of deal.
Brake design makes a difference, so does the amount of gas exiting the muzzle based on the cartridge.
Like you probably won't notice anything with a 6mmCM with 26" barrel and a 308 bored brake, not enough gas getting caught to mitigate recoil.
I've tried the same brake on a 7mm Rem with 26" barrel that was 308 bored and didn't do much, put it on a 300mag with 26" barrel and it was gold.
Too tight where the bullet may deflect is no good.
Too big if there isn't enough gas is also no good.
There is a sweet spot, and yes, I watched the MDT vid, but take it with a grain of salt as they are selling these things lol
 
woodchopper said:
So I've been experimenting with building muzzle brakes and how tight I can cut the clearances to.

I have always assumed that tighter is better, but there is a limit to how accurate you can be.

over the weekend I tried a 243 with the brake drilled out to 0.250" so that's only 0.007" or average 0.0035"

it was too tight of tolerance and tagged the brake.

So I got to thinking how much clearance is there on a commercial brake, I measured one and on a 7mm (.284) the brake was .305" so 0.021" or average 0.0105" so a lot more then what I was thinking.

what is the consensus on how much clearance is needed ?
Click to expand...
The reason you are having issues is because of the run out on your lathe.

Most brakes, IMHO, have too much clearance to be optimally effective and may even deteriorate accuracy because of it.

I've had similar issues as the one you write about. Finally, I decided to try a different method of brake attachment.

I turn a copper or bass rod with two dimensions, one with the exact minor diameter of the bore and another .004 larger.

Then I make up a brake with a bore diameter to match the larger diameter of the rod, and another diameter to exceed the diameter of the OD of the barrel at the muzzle by .002.

I insert the rod into the bore, then slide the brake over the larger diameter and over the muzzle as far as it will go.

Then, I solder it in place.

This keeps everything perfectly aligned to the axis of the bore, and the rod is easily pulled out after everything has cooled down.

The only drawback is the brake is a semi permanent attachment and can't be removed, other than with heat.
 
Another thing to consider is the buildup of fouling in your brake, extremely tight clearance increases risk of a bullet strike unless you're cleaning it regularly.

I thought about it a bit and realized that 0 clearance brakes are possible, but most people refer to this as barrel porting. You'd be limited to a "pepper pot" style brake instead of the chamber type brake.
 
Over the many years I installed brakes I ended up dialing the bore in, threading for the brake and then while the brake was on the barrel would bore the clearance... a minimum of 20 thou clearance, or up to 30 thou. (Total clearance) This resulted in the best accuracy. I have seen factory brakes on prethreaded barrels with over 50 thou. They may need that much or more because of the inaccuracies mass producing and prethreading. At any rate more clearance is better than too little if bullet contact is the result. I made two diameter bore spuds to check brake clearance. One half was bullet diameter, the other slide loosely in the bore. 5 thou clearance was too tight. The bullet may not touch the brake but the super tight tolerance affected accuracy. A larger clearance did not seem to affect brake performance.

Concentricity is all important with close tolerances.
 
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Hitzy said:
20thou is pretty tight IMHO, but doable by a talented Smith, requires some serious alignment and boring concentric to the bore.
Commercial brakes have to deal with factory rifles with possibly off center bores, so they generally go on the larger side, 40-50 thou sort of deal.
Brake design makes a difference, so does the amount of gas exiting the muzzle based on the cartridge.
Like you probably won't notice anything with a 6mmCM with 26" barrel and a 308 bored brake, not enough gas getting caught to mitigate recoil.
I've tried the same brake on a 7mm Rem with 26" barrel that was 308 bored and didn't do much, put it on a 300mag with 26" barrel and it was gold.
Too tight where the bullet may deflect is no good.
Too big if there isn't enough gas is also no good.
There is a sweet spot, and yes, I watched the MDT vid, but take it with a grain of salt as they are selling these things lol
Click to expand...
Obviously you didnt watch the video posted here by Ultimate Reloader!! Im just guessing but highly doubt you used the same equiptment in your testing as what they used. Your brain can tell you whatever you want it to. Your 308 brake was also not bored 308, just sayin. I have a really hard time believing the brake did nothing on your 7MM but was GOLD on the 300. You realize that .308 less twenty thou is .288 and 7mm is .284, yet you stated 20 thou was pretty tight! Maybe you had a sore shoulder the day you tested it on the 7MM.
 
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