Can anyone explain to me as to why when there's a large gap between a muzzle crown and the first port of the brake why the accuracy of the rifle can be reduced? I noticed on the surefire brakes accuracy was less than stellar, took the brake off and put on a quality brake and accuracy went right back to 1/4 moa. There was probably .325 or more of a gap between the crown and back side of the brakes first port. My assumption is the muzzle gas is trying to get around the bullet and enter the bore of the brake causing inconsistencies. Haven't been able to find much on the subject. Thanks for the help guys.
Gunsmithing Intricacies of muzzle brakes
- Thread starter hunter223
- Start date
Why do you think the critical detail is the distance to the first port? I'm not saying it isn't, but why have you focused on that particular detail instead of any other features of the brake?
There are several other possible causes for poor accuracy in a brake, such as crooked threads, off center bore hole, or even an overly thick wall section the bullet passes through. A very tight brake bore hole is more sensitive to all of these as well, than a larger bore.
There are several other possible causes for poor accuracy in a brake, such as crooked threads, off center bore hole, or even an overly thick wall section the bullet passes through. A very tight brake bore hole is more sensitive to all of these as well, than a larger bore.
Because I dialed in the threads of the muzzle concentric to the bore and I made sure that there was at least .020" overbore in the brake vs bullet diameter and I cleaned up bore concentricity to be aligned with the barrel bore. yeah I've read the article by Roy Bertalotto and know what you're saying. I seem to be picking up some skepticism from GH41 that the rifle is a 1/4 moa shooter and that's ok. The rifle is on a surgeon with bartlein barrel 7.75 tw in manners mini chassis it'll consistently shoot factory stuff better than 3/8 and copper creek stuff sub 1/4. Before you try and say that it's because it's a 7.62mm brake on a 6 creed, I tried two other brakes that were 30 cal and did the same thing with them to dial in the bores etc. not that I couldn't be missing something but it seems like things are pointing to that design difference
If your clearance is good I would best it has to do with the harmonics the surefire produces rather than the gap.
then why would a very closely weighted brake of a different design give such different results?
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OK, sounds like a valid reason to suspect the gap, thanks for clarifying. I haven't encountered that with any of the brakes I've built or bought, but have seen gas do some weird things to accuracy. It could be that spacing the baffle either farther forward or farther back would both work better, hard to say without experimenting.
I have seen slanted baffles in a brake mess up accuracy, but I attributed that to the slant, not baffle spacing.
On some brakes, I've cut a cylindrical portion forward of the threads to push the crown out to the rear baffle. Doesnt seem to hurt anything. Looks odd, and is more work. I like Nathan's brakes because he threads them way out into the first port.
Close doesn't count unless you are playing horse shoes. Like I said earlier... Maybe your barrel just doesn't like it.
Watch a rifle fire under high speed footage once. The projectile always outruns the gas plume.
Always. . . So, so long as the brake is effectively altering the direction of the plume, it's working.
Now look at barrel tuners. Small changes in rotation has a potential big influence. There's an easy way to visualize this:
Get a ruler and clamp it to a table. Give it a smack and watch it bounce back and forth. Now move it in or out a little bit and repeat. Assuming you hit it the same way the frequency (number of times it bounces per second, minute, hour, whatever..) alters. Modulation (how far it actually moves from top of the wave to bottom) also changes. This would describe a longer barrel vs a shorter one. Get a thicker ruler and it emulates a larger OD barrel vs a skinny one. If we were to tape a dime and then a penny on the end, it would change again. (pun!) They are both similar in weight, but not identical.
Using this think about the load (cartridge load). Alter the load slightly in the effort to find the "node" where the barrel (ruler) is motionless. Add/remove, increase/decrease length, add/remove barrel mass and it's very possible for you to have to go back and bump or pull back the powder charge.
These are gross generalizations but hopefully they help illustrate the idea.
For a further visual aid. Look at a 50 vs 55 grain bullet. Pick up each and judge one over the other based on weight. Bet $100 no one can tell the difference in 5 grains yet down range there's a remarkable difference.
The forces at play here are not trivial.
Always. . . So, so long as the brake is effectively altering the direction of the plume, it's working.
Now look at barrel tuners. Small changes in rotation has a potential big influence. There's an easy way to visualize this:
Get a ruler and clamp it to a table. Give it a smack and watch it bounce back and forth. Now move it in or out a little bit and repeat. Assuming you hit it the same way the frequency (number of times it bounces per second, minute, hour, whatever..) alters. Modulation (how far it actually moves from top of the wave to bottom) also changes. This would describe a longer barrel vs a shorter one. Get a thicker ruler and it emulates a larger OD barrel vs a skinny one. If we were to tape a dime and then a penny on the end, it would change again. (pun!) They are both similar in weight, but not identical.
Using this think about the load (cartridge load). Alter the load slightly in the effort to find the "node" where the barrel (ruler) is motionless. Add/remove, increase/decrease length, add/remove barrel mass and it's very possible for you to have to go back and bump or pull back the powder charge.
These are gross generalizations but hopefully they help illustrate the idea.
For a further visual aid. Look at a 50 vs 55 grain bullet. Pick up each and judge one over the other based on weight. Bet $100 no one can tell the difference in 5 grains yet down range there's a remarkable difference.
The forces at play here are not trivial.
neither has any other rifle I've put it on with varying barrel lengths.
"Maybe your barrel just doesn't like it" is no help, gives no explanation as to what could be the issue. I don't see how two brakes less than an ounce difference could account for a 1.25 moa difference in group size. How could it? When I take a bare muzzle and shoot 1/4 moa then put another brake on there and shoot at least as well then put a brake on that's less than half an ounce lighter than the first one and it opens the group from 1/4 moa to 1-1/2 moa? Don't think so. I think there's something else going on
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At the muzzle 1oz difference can have a tremendous effect on barrel harmonics. Tuners weigh only a few ounces, yet turning them in or out by less than a rotation yields several nodes. Checkout ad nausea in depth analysis at varmintal website.
then I would think something as minor as adding or removing a thread protector would cause big changes, it didn't. I could understand if we were talking 1/4 moa to 3/8 moa accuracy but were talking about 1/4 to 1-1/2 moa. One of the guys that taught me is a bench rest smith and shooter and has taught me a lot about tuners. He and I have had this discussion and we both came to the same conclusion separately. Does anybody have any research on the gap between the muzzle and first port?
This would be the only way to rule out any other variables, and it would be an interesting test. I install a lot of Holland''s QD brakes- and they specifically call for the tenon to be cut to the length making the muzzle flush with the rear of the first baffle (varies, tapered brake). After that part's been evaluated, I'd like to see a comparison of felt recoil / muzzle rise reduction based on bullet clearance.
It's always stated that minimizing clearance to .020-.030 is mandatory for effectiveness- but I have doubts that this too, is one of the "minutiae" that we get lost in the weeds over. I suspect that the larger the clearance, the greater the volume of gas that escapes directly behind the bullet instead of being directed to the baffles; but really, how much difference can an extra .020 make? It would be nice, to just bore all brakes from 6mm to .30 cal a single dimension, like .3040 instead of splitting hairs.
I've had this book in my "wish list" forever, one of these days I need to get it and find the time to read it, even though I don't fabricate them.
http://www.brownells.com/gunsmith-to...20-105126.aspx
I agree with you, and in my experience building brakes, you are correct - a larger bore doesn't make that much difference, within reason. I've found .30 cal or even .358 cal bored brakes to be very effective even on small calibers like 243 (not that it's really needed, but that's not the point).
One thing though about your comment - if you're making a 30 cal brake, it does need to be some amount larger than .308", and how much depends on distance between the baffles and the muzzle. For a longer brake, I'll go with ~.350-.360" to be sure.
I have a much simpler explanation, ie, the Surefire brake is crap. OK, a "softer" way to put it; the design of the Surefire is flawed. Just my opinion but I have run a half dozen different brakes on my competition AR'S and the Surefire was the poorest performer by a wide margin, a very old design.
Can you expound on that in detail as to why? What design features make it crap? I agree just curious as to your reasoning. A buddy and well known and respected gunsmith on this forum brought up an excellent point this morning. The surefire is a compensated brake. Stands to reason the ports allow gases to excape from the top of the brake causing uneven gas pressure on the back of the bullet. Also we discussed the possibility that the Venturi effect of the chamber from muzzle to front port is causing the gases to speed up and try to make their way around the bullet as it is in the first baffle bore hole. Perhaps the bigger that gap is the more pronounced the effect? I've got an idea given to me of a better experiment to try and get to the bottom of it. I think the harmonics theory is too simple and not looking into the issue deeply enough.
Not being an engineer I'm not sure I can give an explanation as to the "why" other than just through observed results. The Surefire allowed more recoil impulse compared to my other brakes. It's been so long since I turned it into a paperweight I can't recall the specifics of compared accuracy results with the other brakes other than than the overwhelming rememberence & resulting conclusion to forever shelve it. I believe Michael Voight was a principle in the design of the Surefire. While he was a leader in 3-gun competitions and practical pistol, he was no design engineer. The Surefire came out during the height of his shooting popularity as well as during his tenure as President of USPSA. That may have had a lot to do with the early popularity of that brake.
Is this your gun, or someone else's? This is what i was describing in my other post. Ive done this to varying degrees depending on the brake. This was for a little bastard if I recall. In this case, the crown actually extends into the the port area slightly, and the rearward angle at the circumference matches the rearward angle of the port. Somehow I forgot to take a pic with the brake installed. Doesn't seem to hurt anything. I just did it because I like the muzzle to be out near the rear port edge.
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Is this your gun, or someone else's? This is what i was describing in my other post. Ive done this to varying degrees depending on the brake. This was for a little bastard if I recall. In this case, the crown actually extends into the the port area slightly, and the rearward angle at the circumference matches the rearward angle of the port. Somehow I forgot to take a pic with the brake installed. Doesn't seem to hurt anything. I just did it because I like the muzzle to be out near the rear port edge.
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Verryy tricky...
I feel the same way. I have never had great success with surefire on any precision platform, but on a battle rifle 5.56 or 7.62/.308 I think they are fine because I believe that is what they were designed for. There are so many muzzle devices out there that are better choices.
I think @longrifles, Inc gave a very good explanation. Try a better brake for precision instruments such as your surgeon.
Is this your gun, or someone else's? This is what i was describing in my other post. Ive done this to varying degrees depending on the brake. This was for a little bastard if I recall. In this case, the crown actually extends into the the port area slightly, and the rearward angle at the circumference matches the rearward angle of the port. Somehow I forgot to take a pic with the brake installed. Doesn't seem to hurt anything. I just did it because I like the muzzle to be out near the rear port edge.
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Good looking thread job
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