Muzzle Brakes and harmonics

G

gstprecision

Regular
Rating - 100%
13   0   0
Location
Frankford, On
Never been much of a muzzle brake guy. Recently I finished building a 7mm-08 for my son. Savage action, Shilen 26" SS Heavy barrel. He wanted to have a muzzle brake on it. So I threaded the muzzle end and installed a brake then single point bored it to 0.020" over caliber nominal.

Went to the range and broke the barrel without the brake. After we were happy we put the brake on to see how it performed. Well the recoil reduction was great, but the most noticeable feature was the muzzle lift reduction, we could watch the target as we shot.

The problem I immediately noticed was the POI shift. I went about 9 inches high at 100 yds. The group sizes stayed the same.

Came back home took everything apart, inspected the brake for obvious bullet strikes but no signs. I decided to re-bore the brake to 0.030" over caliber nominal to ensure there was no slight bullet strikes.

Went back to the range shot the rifle without and with the brake on, same results 9" POI shift. Again no change in group size.

I know adding weight affect the harmonics of the barrel and changes the nodes, but I never experienced anything crazy like that before.

Any ideas/suggestion/experiences to share.

GST
 
Barrel harmonics can only account for POI changes of small fractions of an inch at 100 yards. With a 9" change there must be a lot more going on than that...
 
Perhaps the axis of the barrel bore is not linear with the break. Its one thing to be concentric at some plane, but another to be in line axially... Rotating the brake 180 degrees and firing it would tell you something.
 
Yeah 9 inches is crazy at 100 yds. I will try rotating the brake, never thought about that.

The threads were made concentric to the bore, indicated off the lands. The original boring of the brake was done when installed on the barrel.

If everything fails I will take the barrel off cut it and rethread the rebore another brake.
 
The barrel is a giant tuning fork. Add any metal to the end of it and you are going to change that harmonic. This is obvious. Altered harmonics is gonna change POI.

The brake alters gas flow out the muzzle. Gas flow is involved in the generation of recoil and muzzle flip. Those things are gonna alter POI.

Your brake moved POI up but otherwise did not change group size. This is a win-win situation. The POI being higher will allow longer range as it increases the number of MOA available in the optic. Essentially you have created a 10 MOA rail for free. Why would you want to correct this?

FWIW .030" over bore size is very small. That leaves only .015" clearance between the brake and the bullet. You should go up to roughly .050" over bore size. That will give a bit better margin of clearance.
 
If the brake is concentric to the bore, 50 thou over bullet diameter definitely is not required. I bore my brakes 20 thou over bullet diameter for most efficient performance.

If it groups well there is enough clearance... more clearance does not improve it... if there isn't enough clearance accuracy is the first thing to suffer...
 
Yes it does group well with and without the brake. I still need to find the best load for this particular rifle, I am waiting for the stock to come in. When it is all installed and bedded I will start developing the load for it.

I will go back to the range this week and rotate the brake 180 degree see if I get the same results, or a POI shift 9 inch low.

Suputin, I like the way you think. I am running a bit short on the scope adjustment, it is mounted on a 25 MOA base already, but I will change the scope anyway, I just put a scope that was laying around doing nothing for now.

GST
 
I don't have enough experience with gunsmithing to really carry any huge merit to my opinion, but I have a feeling the 20 thou is too tight, maybe it effects the way its "crowned" or how the gasses pass around it as it passes through the ported section of the brake, or if the ported openings in the brake are not equal the gasses pass around the bullet differently giving it a cant to one side. It would be nice to have a different brake so you could compare, but I think the easiest thing for you to do is to open it up a bit first.

Alternatively, an equal sized (or weight) piece of steel on the end of the barrel to see if it repeats the results might tell you more.

It could be right at an opposite node, which I would think would give it mostly a vertical change, though obviously you wouldn't think it would be that much with heavy contour.

Weird, and neat.
 
Most of the guns I built were made for a brake per customer and I don't know if POI changes with or without.
One of my AR 15 I tried with a new brake made a 4" POI change high and left slightly @ 100yds. This a free floated standard GI profile barrel if it helps.

I'm going to build another bolt gun for myself shortly and try it with/without.
 
cody c said:
I guess I'm out to lunch on the 20 over
Click to expand...

You are... If the brake is of decent quality and bored on the barrel concentric to the bore, 20 thou clearance has proven to be adequate for over 45 years of making brakes personally.
 
I made up a brake for my hunting rifle last fall. Guntech is certainly correct about the bore of the brake being concentric to the bore of the barrel. I had tried another brake on the same rifle and wasn't happy with it. IMHO it didn't reduce recoil enough and the way it was designed created all sorts of turbulence all around the muzzle area. Accuracy was OK but I ended up developing a flinch from the noise and flying debris.

The rifle I was using was a Brazilian Mod 1935 Mauser chambered in 7x57. The original barrel length of 29in made it to long but still mounted the brake to check its efficiency. Not nearly good enough IMHO. It had .020 clearance and it was mounted perfectly. Still, I wanted more.

I made up a brake on my lathe and milling machine that was more to my liking. The first thing I did was cut back the barrel length to 24.5 inches. Then I weighed the bit I cut off. The great thing about those old military mauser barrels is that they are stepped to enhance harmonics. It is a great system that works very well. Adding the weight of a muzzle brake onto the end of a barrel changes all of the tech that went into those steps. The new brake doesn't have any holes on the top or bottom. It weighs exactly as much as the stub I cut off the end of the barrel. The bore of the brake is machined to have .002 clearance all around the bullet while it's in the brake. Many of the commercial brakes have a large expansion chamber after the barrel muzzle and a tight exit hole with multiple holes drilled 360 degrees all around. My brake has two lines of holes down each side of it 180 degrees to each other.

The brake was machined from a piece of cold rolled round stock. No threads were cut on the brake or the barrel. I believe those threads just create more un needed stresses. It could all be just a theory as well. I used the milling machine to drill all of the exhaust holes and then removed metal from the top and bottom as well as two channels on each side encompassing the exhaust holes to get the brake down to the weight of the barrel stub I had removed.

Then, I made up a brass spud to fit snugly into the bore of the muzzle and the bore of the brake. When it came time to mount the brake, this spud was crucial to keeping everything concentric to the bore. I then silver soldered on the brake. It works extremely well. It is much more effective than the commercial brake IMHO.

I will however admit that it would be prohibitively time consuming for a commercial smith and extremely expensive for a customer. My design works well but would not be fiscally viable for most shops. I only have my time to consider. A smith has to consider what sort of return he can make from any job he tackles.

There is a young fellow just out of Nelson that is making up some lovely brakes on his CNC equipment for very reasonable prices. I will be seeing him in April at the Nelson Wildlife gunshow and intend to purchase one from him to try on another build I'm working on.

Now some will ask why I need a brake. I also need a couple of new shoulders and recoil causes severe pain which leads to flinching. Brakes have their place for someone with such afflictions. I have seen some of guntech's work, the man does a very good job. He knows his stuff.
 
Last edited:
A&Shuntr said:
Seems like a strange statement coming from a company that promotes making muzzle brakes - doesn't instill much confidence...
Click to expand...

I see your point. I personally never been a fan of the side blast and concussion. But after installing one on this rifle, I see the huge benefits. The recoil is certainly reduced by a good amount, but where I found the brake to perform extremely well was in the reduction of muzzle lift and tracking in line. I could watch the target and not loose it in the scope as I took my shots.

Still not a fan of the concussion, especially if you are on the side at the range, but for everything else the brake provides I am now slowly changing my opinion. I will now install some on my heavier caliber rifles for sure.

GST
 
I put a Grizzly Gun Works clamp on muzzle brake(Ghost) on my Tikka T3 SS varmint and is was made from Stainless and it was a heavy brute and it did not change a thing and all this talk about Harmonics.
 
I have received many emails from clients that have installed the brakes and they all said the POI change was either not there or less than 1 MOA. I am unfortunately the only one having problems. As I said I might be dealing with multiple issues here. Rifle not bedded, flimsy stock possibly touching the barrel when firing, and harmonic changes from the brake....

I found a couple of good technical article on varmintal demonstrating barrel harmonics. Good read to get a good understanding of what's happening with added weight and length of a brake.

I will fix the obvious, stock and bedding, confirm the alignment of the brake then head back to the range for more testing.

GST
 
I have seen significant changes in POI with the installation of a brake but have never seen anything like 9 inches. I have seen four inches. I have always tried to make the thread-protector to weigh close to the same as the brake to minimise changes and this has seemed to work. I also think .020" clearance is plenty if the installation is well done.
I
While I am also not a huge fan of brakes, I do recognise the benefits for some shooters. I was a huge fan of the money I could make by making and installing them ;)
 
Sorry if this has ben covered, but what or how did you check to make sure it was concentric with the bore, in my mind even if it has a gap between the projectile and the body of the brake, if it isn't centered the gasses passing by it at tens of thousand of psi could have an effect on canting it as it leaves the barrel. Or if one of the ports was closer to the muzzle, it could greatly change the way the gases pass around it.


Would be cool if someone had one of the super high speed cameras to record a bullet leaving the ned of it to see...
 
You must log in or register to reply here.
Back
Top Bottom