Muzzle Brakes and Harmonics

G

gstprecision

New member
I just finished building a rifle for my son. Savage action with a Shilen SS 26" Heavy barrel in 7mm-08. We went to the range to break it in and test it out. It shoots really well.

My son wanted to have a muzzle brake on it so I threaded the muzzle to accept one. After initial break in I installed the brake and to my surprise the POI shifted by 9 inch high. Grouping size stayed the same. I have never used muzzle brakes before so I did some research and still not sure about this.

Came back home, took the brake off and inspected, no signs of bullet strikes. I re-bored it from 0.020" to 0.030" over caliber nominal to make sure there was no bullet strikes, returned to the range and same thing when installing the brakes.

As I said I have never used brakes before so I am kinda clueless. Can the harmonics of the barrels be affected that much to cause a 9" shift up on POI after installing a brake? Or am I missing something here?

I wanted to run more test using some Lead Tape and duplicating the added weight of the brake to see if I get the same shift.

Any suggestions/ideas/experiences?

GST
 
if the group size stayed similar, then do not worry.
my GUESS is you are at the end of a node, and the small
change in harmonics is the issue.

i bore my brakes on the bbl, the the brake bore is inline
with the bbl bore.
 
I am running short on scope adjustment, it is mounted on a 25 MOA base already.

While replying on another forum I realized on thing. I am waiting on the stock to arrive, it is now temporarily installed in a flimsy Savage Tupperware stock. I did not check the clearance when it is sitting on the bipod. I might have a combination of a few things here.

I will make a few loads and head to the range this week, if weather cooperate, it was suggested to rotate the brake 180 degree to see if I get a shift in the opposite direction. I can try that and blame myself for the bad threading/boring of the brake...LOL

GST
 
If you remove the brake, does the POI drop back 9"?

I just finished a brake too, but it's in 585-caliber. Still needs final polishing but it'll get tested soon. I'll see if the impact changes much on versus off and report back.





-Lee
www.singleactions.com
 
There is never a vibration node at the end of a barrel.

Adding mass to the end that is NOT bore diameter CAN result in a node at the end of the bore diameter part of the barrel.

A muzzle break can provide the extra larger than bore mass to move the node away from the end of the break.
 
gstprecision said:
Yes it goes back down to the original POI.

Nice work on the brake should work good.

GST
Click to expand...

Wow...9 inches! That is a bunch! I've done a bunch of brakes and I make tuners...so, I have done a lot of testing. That's more than I've ever seen. Certainly not saying it isn't possible. I just think gun harmonics are interesting...and how they relate to what we do.
 
I am gonna start eliminating the obvious first. I believe the stock might be hitting the barrel, it is a flimsy Savage Tupperware. I am waiting on a Boyds Laminated. Going to bed it.

In the meantime I will take the barrel off, need to paint it, and chuck it in the lathe and take some measurement to make sure I did not screw up the threading, then measure the brake on the barrel.

I might take it to the range one more time before disassembly and try rotating the brake 180 degree see what I get.

Thanks for the replies.

GST
 
When you put the barrel back up in the lathe, indicate the bore just behind the crown and then as far back as your indicator will reach. Make sure both places run true. At that point, indicate the shoulder where the brake seats at the end of the threads for perpendicularity. Then reinstall the brake and indicate the bore of the brake near the end to see if the clearance hole is true to the bore. You may also want to indicate the o. d. in a couple different spots along the length to see if it has any wobble which would show thread projection squareness.
 
Thanks Rflshootr, That is about what I was going to do, but you added a few more steps I did not think about and they make a lot of sense.

GST
 
gstprecision said:
I just finished building a rifle for my son. Savage action with a Shilen SS 26" Heavy barrel in 7mm-08. We went to the range to break it in and test it out. It shoots really well.

My son wanted to have a muzzle brake on it so I threaded the muzzle to accept one. After initial break in I installed the brake and to my surprise the POI shifted by 9 inch high. Grouping size stayed the same. I have never used muzzle brakes before so I did some research and still not sure about this.

Came back home, took the brake off and inspected, no signs of bullet strikes. I re-bored it from 0.020" to 0.030" over caliber nominal to make sure there was no bullet strikes, returned to the range and same thing when installing the brakes.

As I said I have never used brakes before so I am kinda clueless. Can the harmonics of the barrels be affected that much to cause a 9" shift up on POI after installing a brake? Or am I missing something here?

I wanted to run more test using some Lead Tape and duplicating the added weight of the brake to see if I get the same shift.

Any suggestions/ideas/experiences?

GST
Click to expand...

I've experienced a number of thin "hunting style' barrels of #4 taper and smaller shift as much as 6moa in random directions just from changing loads so IMO this isn't unusual. Especially if you've an over-sized (larger than barrel diameter) brake. And it's certainly nothing to be concerned with (altho if you turned the brake 180* as suggested, and poi moved with it, THEN you've a real problem!!)

BTW very few target/BR shooters ever mess with barrels smaller than #5 taper :)
 
I used a fitted pin last night, I had to add 1 layer of scotch tape to make it tight, and it look like everything align and the brake hole was concentric.

I got some small brass bar today from work and I will machine it down to make a perfect fit and reconfirm the alignment.

Alinwa, thx for your feedback. I will definitely try the upside down brake and see the results.

Side note, I really appreciate this forum so far. Other forums I go I would have had 20 non-sense reply by now, and all the drama that goes with it. I don't know if this is the norm, but getting good feedback and constructive replies is refreshing. I will definitely be hanging more around here.

GST
 
gstprecision said:
I used a fitted pin last night, I had to add 1 layer of scotch tape to make it tight, and it look like everything align and the brake hole was concentric.

I got some small brass bar today from work and I will machine it down to make a perfect fit and reconfirm the alignment.

Alinwa, thx for your feedback. I will definitely try the upside down brake and see the results.

Side note, I really appreciate this forum so far. Other forums I go I would have had 20 non-sense reply by now, and all the drama that goes with it. I don't know if this is the norm, but getting good feedback and constructive replies is refreshing. I will definitely be hanging more around here.

GST
Click to expand...

You have found the one forum on the net where a few of us would rather be kicked off or deleted than feed you pap and unfounded opinion...

replies/membership are fewer and in constant flux but on the whole rawther more useful than anywhere else.....this is THE ONLY forum on which I'll post an opinion.

Period.
 
No, did not have time, I had some work to finish and I took the rifle apart for finshing, it needs to be painted with KG Guncoat.

GST
 
Well... I went to the range last weekend to sight in my coyote rig and could not keep itnon paper...... I used the same scope as I had on my 7mm-08, returned home put another scope on the 223 and perfect.

The scope is definately pooched, pretty sure it accounted for the above average grouping I had with the -08. Might just have been a fluke that when I put the brake it shifted 9"...... More testing to be done with a good scope.

GST
 
I was shooting a .28 Mosler last week. Changing from a suppressor to a Badger Ordnance brake dropped point if imoact 3". I don't know what the change would have been from bare muzzle to brake as had no desire to shoot it without some kind of braking. Accuracy wasn't changed. So pretty well is similar to what you experienced. I've thrown away a lot of the plastic factory stocks.
 
Mike Bryant said:
I was shooting a .28 Mosler last week. Changing from a suppressor to a Badger Ordnance brake dropped point if imoact 3". I don't know what the change would have been from bare muzzle to brake as had no desire to shoot it without some kind of braking. Accuracy wasn't changed. So pretty well is similar to what you experienced. I've thrown away a lot of the plastic factory stocks.
Click to expand...

And I'm guessing the suppressor was heavier than the brake?
 
Mike Bryant said:
I was shooting a .28 Mosler last week. Changing from a suppressor to a Badger Ordnance brake dropped point if imoact 3". I don't know what the change would have been from bare muzzle to brake as had no desire to shoot it without some kind of braking. Accuracy wasn't changed. So pretty well is similar to what you experienced. I've thrown away a lot of the plastic factory stocks.
Click to expand...

As Al, I'm assuming the suppressor and brake don't weigh the same. This isn't out of the norm, IME, for the poi to change that amount. And, it's entirely possible to have very near same accuracy, even with considerably different weights, but that isn't necessarily the case. It can be and I take your word for it that it is. That said, it can also take very, very little weight to make a considerable difference in accuracy. The are multiple weights and tuner positions that are in tune, so it can certainly be the case with your example. No different than moving a tuner a few clicks and being back in tune, from another "in tune" setting. Accuracy relative to tuners and other means of weight at the muzzle is about timing bullet exit with muzzle position. It happens frequently...not just at a given weight or singular tuner setting.
 
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