Gunsmithing Fitting a muzzle brake

[dareposte]

So I had made and fitted a muzzle brake to my 338 Edge, but despite my careful machining I shot it the first time out. Just a slight glancing blow to the last baffle, but it would probably not help my accuracy to leave it.

I had made the mb hole 0.358" diameter, (20 thou oversized) since that's what is supposed to work the best.

I measured a factory Remington 700P / 338 Lapua brake and the hole in it is like 0.400".

What do you think, is 0.020" oversize too tight? I'm bummed it didn't work out but I guess I get to learn something today.

FWIW, the machining error I made was assuming the drill bit will drill a straight hole. The brake was about 3.5" long end to end and the bit wandered 0.025" over the course of the initial pilot hole.

 

[deadeye]

Re: Fitting a muzzle brake

The .020 over is correct, what you need to do is finish bore it in a lathe not drill it - never trust a drill to go straight.

Indicate off the bore, screw on the brake, pop an under size hole, then cut the ID .020 over with a boring bar.

This allows the brake to have perfect bore alignment inside.

 

[Hateca]

Re: Fitting a muzzle brake

+1

Never ever use a drill bit to finish bore a hole. Boring bar is the best or even a piloted muzzle brake reamer.

 

[dareposte]

Re: Fitting a muzzle brake

I guess I need a new boring bar, I don't have anything remotely close to fitting into a 0.30" hole that will extend far enough in to be useful.

I did use a reamer to finish the hole though, so I guess I wrongly was hoping that it would straighten up any small deviations.

I was thinking about drilling the hole first, then holding it between centers and turning the OD, then threading and fitting it to the gun. It would at least average out the errors I think so the wandering drill hole would have less impact. But from the knowledgable guys here it still wouldn't be a good idea to do it that way.

maybe a gundrill? If I use a boring bar I'll definitely need to redesign the brake as it's got a couple baffles in it right now that just won't be doable to machine it with that much overhang on a tiny boring bar.

For reference here's the design I'm referring to:

 

[300sniper]

Re: Fitting a muzzle brake

i make my brakes with an undersized through hole and then bore them .020" over bullet diameter on the barrel at the same time as i'm cutting the muzzle threads.

chances are, like you found out, that a drill will wonder. using a boring bar is the way to go. boring a .358" hole, 3"+ deep may take a homemade tool.

 

[300sniper]

Re: Fitting a muzzle brake

if i had to make the hole concentric to the brake threads independent of the barrel, i would place a piece of round material in the lathe with a short stick-out. i would then turn/thread it so the brake screws on. without moving anything, i would screw the brake on hand tight and bore the exit hole.

 

[Wild_Bill]

Re: Fitting a muzzle brake

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: deadeye</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">if i had to make the hole concentric to the brake threads independent of the barrel, i would place a piece of round material in the lathe with a short stick-out. i would then turn/thread it so the brake screws on. without moving anything, i would screw the brake on hand tight and bore the exit hole. </div></div>

The trouble here being that the bore is rarely concentric with the OD of the barrel. So if you cut the barrel threads concentric with the bore, the OD - usually cut on a taper as this design is - will never give a prefect match to the barrel.

The only option is to turn barrel threads concentric to the OD of barrel then bore exit of the brake concentric with barrel bore.

</div></div>

I understand your thinking but it is wrong never do it that way what happens if someone then replaces your break down the track with an off the shelf break or supressor they will end up in trouble the threads MUST be concentric with the BORE not the OD of the barrel if it takes a little to make the finish look presentable so be it but it is more inportant to have the bore and thread centred.

 

[dareposte]

Re: Fitting a muzzle brake

What barrels are you guys working on where this is even a problem? Every barrel I've ever bought and checked has been profiled between centers and is pretty darn close concentric OD and bore at the ends.

I guess a factory barrel might not be?

 

[300sniper]

Re: Fitting a muzzle brake

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Wild_Bill</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: deadeye</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">if i had to make the hole concentric to the brake threads independent of the barrel, i would place a piece of round material in the lathe with a short stick-out. i would then turn/thread it so the brake screws on. without moving anything, i would screw the brake on hand tight and bore the exit hole. </div></div>

The trouble here being that the bore is rarely concentric with the OD of the barrel. So if you cut the barrel threads concentric with the bore, the OD - usually cut on a taper as this design is - will never give a prefect match to the barrel.

The only option is to turn barrel threads concentric to the OD of barrel then bore exit of the brake concentric with barrel bore.

</div></div>

I understand your thinking but it is wrong never do it that way what happens if someone then replaces your break down the track with an off the shelf break or supressor they will end up in trouble the threads MUST be concentric with the BORE not the OD of the barrel if it takes a little to make the finish look presentable so be it but it is more inportant to have the bore and thread centred.

</div></div>

you took the words out of my mouth bill.

if the brake needs to be blended to the barrel or appear to be "one unit", the threads should first be cut concentric to the bore, brake installed and exit hole bored, then adjust the setup to be true to the od of the barrel and blend the brake.

 

[WTW]

Re: Fitting a muzzle brake

tag-

I am going to try making and installing a brake in the near future. Great reference. I like the style of your brake it looks like it should work excellent.

 

[Hateca]

Re: Fitting a muzzle brake

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dareposte</div><div class="ubbcode-body">What barrels are you guys working on where this is even a problem? Every barrel I've ever bought and checked has been profiled between centers and is pretty darn close concentric OD and bore at the ends.

I guess a factory barrel might not be? </div></div>

Every barrel has run-out, even custom barrels, if you are chambering or threading between centers (or using a steady rest without doing some special pre-chambering machining before hand) and you plan on using brakes or suppressors you are asking for trouble.

Measuring just inside the bore to check for run-out is not the correct way to check. Checking a barrel between centers isn't going to tell you the entire story of the barrel and could cause you some major issues if one relies on that information alone.

 

[300sniper]

Re: Fitting a muzzle brake

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dareposte</div><div class="ubbcode-body">What barrels are you guys working on where this is even a problem? Every barrel I've ever bought and checked has been profiled between centers and is pretty darn <span style="color: #FF0000">close concentric OD and bore at the ends</span>.

I guess a factory barrel might not be? </div></div>

the barrel may have been contoured between centers therefore concentric at the extreme ends but what happens when you cut an inch or six off of the blank?

 

[dareposte]

Re: Fitting a muzzle brake

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dareposte</div><div class="ubbcode-body">What barrels are you guys working on where this is even a problem? Every barrel I've ever bought and checked has been profiled between centers and is pretty darn <span style="color: #FF0000">close concentric OD and bore at the ends</span>.

I guess a factory barrel might not be? </div></div>

the barrel may have been contoured between centers therefore concentric at the extreme ends but what happens when you cut an inch or six off of the blank? </div></div>

Point taken, I can see how that could be a problem.

 

[dareposte]

Re: Fitting a muzzle brake

Well I didn't have a boring bar that could make the cut, so here's what I did and it worked pretty well.

1) Center drill one side of the brake blank in the 3-jaw
2) Drill the hole with 5/16" drill bit (it wandered about .020") then ream it.
3) Flip it over and center-drill where the hole came out
4) Support the piece between centers and true the outside (took 0.025" off to true it)
5) Machine the rest of the piece and install on the gun.

How do I know it worked allright? I made a concentricity gage to check it with this time. It basically has a pilot that's 0.330" that fits snugly in the bore, and a bunch of steps from 0.344"-0.358" that should match up in the MB's 0.358" reamed hole. How far it goes into the bore determines the concentricity of the MB's final baffle. In my case it was out 0.002" at the end of the brake, not perfect but acceptable.

<span style="font-style: italic">Picture of the concentricity gauge I made. The pilot on the near end is 0.330", and the steps on the far end step up to 0.358" the ID of the muzzle brake. Slide the pilot into the bore and see how far into the brake hole the gauge will go, and you know the concentricity error. Mine was 0.002" and seems to be fine.</span>

 

[dareposte]

Re: Fitting a muzzle brake

Shot through the muzzle brake tonight, and as it appeared everything lined up fine. The powder blast rings around the baffles looked nice and concentric and the accuracy was okay for a first try with a new load.

Talk about L-O-U-D though... I was shooting with plugs and muffs, and one time left the muffs off (only plugs in) and my ears were definitely ringing.

The kick was greatly reduced as well, its easier on my shoulder now than my 30-06 is with a hot load.

 

[pappy42]

Re: Fitting a muzzle brake

Thanks for the post(s). It helps us dreamers firm up our thoughts and keeps us from making some of the same mistakes