Gunsmithing Proper muzzle Brake Bore

[Ballistic Artist]

Hey all,
Getting ready to install a MRAD brake on my 300WM. I have heard different opinions on boring a muzzle brake. The first one is that the bore of the brake should be the same diameter for all baffles.(Makes perfect sense to me) The second one is that the bore of the first baffle should be bigger and then the bore progressively gets smaller ending with minimum safe diameter at the final baffle. Does the second opinion hold any value or is it a load of crap? Thanks.

 

[FMJBT]

Seems like there might be some sense in having the hole get progressively tighter through each baffle. Allowing a bit more high pressure gas to follow through with the bullet will allow more of it to contact the face of the next baffle in line, effectively "spreading the load" across several baffles. I would think this would be more effective than having the same diameter hole all the way through, as it increases the amount of surface area that gets hit directly by the muzzle blast. The Darkmetal Designs "HK Style" brake I run on a few rifles is set up this way, with the first through hole in the baffles being significantly larger than the next hole down the line. This style of brake is one of the more effective brakes I've run on my rifles.

 

[Massoud]

I did a lot of research on muzzle brakes (the military did the research, I just read the results). There was an optimum bore diameter for efficiency and it didn't involve being overly large at the first baffle. I don't remember a test of a progressively smaller bore diameter though. That could mean they just outright knew that it wouldn't be best due to physics or maybe they just never thought of it.

A shooter on 6mmbr.com did a great writeup that gets reposted every now and then about brake tests for accuracy and I want to say he found that .020" over was the best. You should be able to find it with a search.

I have a theory that at this low level of recoil (relative to artillery and tanks) that there won't be huge detectable (to your shoulder) differences in brake efficiency. This stems from seeing all the wacky designs which run counter to 100 years of military testing from multiple countries, and yet people claiming they're the best brakes they've ever run. One of these days we're going to build a ballistic pendulum and find out which ones on the market are the best.

I will say that there is not a practical need to spread the load to other baffles and in fact the most efficient brakes designed stripped as much gas as possible as quickly as possible and it was found that anything over 2 baffles is really just adding weight for small increase in efficiency.
Justin

 

[DAVETOOLEY]

I will say that there is not a practical need to spread the load to other baffles and in fact the most efficient brakes designed stripped as much gas as possible as quickly as possible and it was found that anything over 2 baffles is really just adding weight for small increase in efficiency.
Justin

I couldn't agree more. There are several goals when using a brake. One to reduce the affect the gas has on the bullet inside the brake and two to reduce recoil by venting gas. Both should be accomplished as quickly as possible. The vast majority of the work is accomplished by the first port. I like .020" clearance per side myself. Leave a little room for crud to build up because it will.

 

[Cncjerry]

Generally, and everyone has their own design, the first baffle near the muzzle is tightest for a number of reasons. The first is that baffle does a lot of the work as mentioned above. Second, It is less risky to strip the air tightly at the first baffle as you are more assured of the alignment with the bore. The farther you go you can widen the baffles as the cone is expanding (or would be). Widening the baffles reduces the risk of a strike as you can imagine the bullet starts to deflect the farther from the muzzle though we are talking 10ths. I've made a lot of baffles and on a small caliber 10 stack, not a brake obviously, I widen them about .005" per to avoid a strike.

Again, as above, most of the work is done in the first baffle and instead of more baffles, and I haven't studied this in detail, I would think a larger first and second baffle would work just as well as five, for instance. It all comes down to surface area and gas velocity balanced against size so you don't obstruct the site picture.

 

[mcfred]

This stems from seeing all the wacky designs which run counter to 100 years of military testing from multiple countries...

What are the basic ideas of good brake design from this testing? In your reading/research, which features make a brake most effective?

 

[308FMJ]

We bore all brakes .020" over at work.
Jim

 

[Massoud]

There's a couple basics that really stood out:
-More than 2 baffles is just adding weight/cost/material for minimal gains
-the 2 port tank style brakes seemed to be the best combo of efficiency and not too much overpressure, the pepper pot style brake was similarly balanced but typically LR shooters don't want to kick up dust.
-There is a specific position for each baffle which is a multiple of the caliber, i.e. 30 cal first baffle should be 2 x .30 from the muzzle. The multiple wasn't necessarily 2 I just can't remember exactly. This multiple changes for each baffle, so if you see a brake which has 5 baffles evenly spaced then that's a good indication that whoever made it was just making things up as they went. Typically the 2nd baffle should be closer to the first baffle than the first baffle is to the muzzle.
-For more efficiency, angle the ports/baffles rearward and ideally make it a smooth curved transition from forward gas travel to rearward travel (this requires a cast or two-piece brake). This greatly increases overpressure though.
-The baffles get more efficient the larger they are (more surface area), within reason. For us we can't go too large on the baffles and I don't think we'd notice much anyway.

Justin

 

[kortik]

There's a couple basics that really stood out:
-More than 2 baffles is just adding weight/cost/material for minimal gains
-the 2 port tank style brakes seemed to be the best combo of efficiency and not too much overpressure, the pepper pot style brake was similarly balanced but typically LR shooters don't want to kick up dust.
-There is a specific position for each baffle which is a multiple of the caliber, i.e. 30 cal first baffle should be 2 x .30 from the muzzle. The multiple wasn't necessarily 2 I just can't remember exactly. This multiple changes for each baffle, so if you see a brake which has 5 baffles evenly spaced then that's a good indication that whoever made it was just making things up as they went. Typically the 2nd baffle should be closer to the first baffle than the first baffle is to the muzzle.
-For more efficiency, angle the ports/baffles rearward and ideally make it a smooth curved transition from forward gas travel to rearward travel (this requires a cast or two-piece brake). This greatly increases overpressure though.
-The baffles get more efficient the larger they are (more surface area), within reason. For us we can't go too large on the baffles and I don't think we'd notice much anyway.

Justin

Justin

Very good summary.

In my own experimentation with MBs, I did find out that adding the third baffle (at certain distance to the second one) seems to add just a bit to felt recoil reduction, while adding the 4th baffle (or more) didn't do anything. However, there is no doubt that the first two baffles are the most important and do the major part of the job of cutting off/redirecting the blast.

I did not experiment with baffle exit holes having different diameters, but logically thinking, it appears not to have any value at all, while complicating production and increasing the cost.

.020" over the bullet diameter is a good number, and close to 0.015" is even better, but then barrel thread should be highly concentric to the bore. If I do both MB and barrel thread, I can get away with 0.015", cause I know my thread will be nearly perfect and concentric within, say, 0.002" to the bore, and MB internal tread will be even better. But when MBs are sold as items for installation by the third parties, 0.020" is a safer bet.

 

[Massoud]

Found the link: Adventures With Muzzle Brakes | RVB Precision
posted on accurateshooter again today
Justin