I removed a muzzle brake from a shot out 270 Wby. Now I have a 7mm that I would like to put it on. The biggest pin that will go thru it is .296". Is that enough clearance or do I need more?? How much more??

It should be OK as long as the ID of the brake is concentric with the ID of the barrel

I thought the min. Was .020 clearance

I would open it up some, I dont think you wanna a baffle strike.

Open it to .324" or is .312 enough?



.020" total or per side??

I would take the brake and throw it in the trash.

I read that wrong, you don't have enough clearance. You need .020" minimum and concentric. SOrry if I misled you.

So is that .020" over bore size or .020" clearance on each side (.040" over bore size)??

.020 over .284 minimum-I prefer .030 over bore size personally and it will not effect efficiency

Seems to me if the original had over .022 over bore size, your 7mm ( .280) would want to be .302 at least. Assuming evrything is concentric.

Ditto..

OK, .312" it is!!

Measure your actual bullets and you will find 7mm bullets are .284". The perfect install with max efficiency is .284" + .020" = .304". The hole is opened up with a small boring bar. A reamer or drill will simply follow the old hole and not be perfectly centered on the bore. Be sure you dial in the last 2" of bore rather than only the exit or with both ends centered. Cut your threads and bore the hole on that setup or risk an off centered hole or threads misaligned with the bore. If you ever decide to use the threads for a suppressor this is the only way to guarantee no baffle strikes.

This barrel was already threaded and I can't cut it shorter w/o getting into the flutes.
On the barrels that I have threaded in the past, I go between centers, cut a clean up pass to center the bore with the OD, then thread. Am I doing it incorrectly?? If the bore is on a center, the clean up cut will make the outside concentric - right?
I don't know what you mean by dialing in the last 2" of bore. An inside indication is going to bump off of the rifling. An outside indication may not be true to the bore. Are you saying use a pin or range rod that is at least 2" into the bore and indicate off of that?

measuring directly off the bore/rifling is the best way to indicate a barrel true to center of the bore. If you don't understand what HiredGun is talking about you might want to research a little more before continuing with your gunsmithing adventures.....

Seems to me coming to the Gunsmithing sub forum and asking questions is trying to research the problem.

CowboyBart. 020" is the total clearance you need for most hunting bullets, (.010" per side) but some of the extra long VLD types should be cleared more. I would go about .035" for them. Some of the have a bit of yaw until the go to sleep and if they touch a baffle it won't harm a thing, but the accuracy will suck.

Keep in mind that concentric mounting with the BORE is needed, not the outside of the barrel if you want close tolerances.

Some smiths don't center on the bore and mount them by locating off the outside of the barrel and that's OK if you give enough clearance, but sometimes you'll need up to .070 if it's done that way.

If the bore is off center in the barrel (not as uncommon as you might think) you can mount them locating off the outside and it looks good, but you need to have clearance on the inside and if you need a lot, the break doesn't reduce the recoil as much.

Myself, I never use the outside of a barrel to locate from. I locate 100% of the time from the bore. In a few cases it will look as if the break is "mounted crooked" with some barrels. This should be explained to the customer before you accept the job. It's the inside that matters.

If a customer has an off-center bore I offer to true the barrel at the time I install a break, but that means a re-finish job too, so I leave it up to the owner of the gun.

But .020" is fine if the bore is centered.

Do you know how to spell "BRAKE?"

oops!

Sorry.




Good catch however

I don't think anyone was asking about or suggesting indicating off the outside of a barrel, anyone except the most inexperienced gun hack should know not to do that.

CowboyBart, when gunsmiths talk about indicating the last 2" of the bore, generally that means to use a close fitting gauge pin or other very straight rod in the bore, and indicate on the rod at the muzzle and a couple inches away. (Obviously the rod needs to be at least about 4" long to do this.) The alternative is to use a long-tipped indicator directly on the bore, and just pay attention to whether you're measuring lands or grooves. You'll need a 4 jaw chuck and a "lathe spider" (like a crude 4 jaw) at the back end of the spindle to do this, or for shorter barrels make yourself a tube that fits in the chuck with 4 jaw adjustments near each end.

Setting up between centers is not technically as accurate because most bores aren't straight. However, the difference is so small that in my experience it doesn't matter for most brake installations. There's no harm in going with .030" or even .040" clearance if in doubt; in my experiments it has made no difference in brake effectiveness but can sometimes be more forgiving which leads to better accuracy.

Any customer sees a so-called 'gunsmith' doing THAT and he/she better grab their rifle back in a nanosecond and beat-feet OUTTA that shop - like, FOREVER...:)

While this one was already threaded.
I usually go between centers and turn the OD concentric with the bore. Then indicated off of the OD. Yondering did mention that this is not the most accurate method, and this may be true.
I am gearing up to use a spider on the lathe, I'm just not there yet. My projects usually take months and even years because I am NOT a gunsmith or a machinist. I do spend the bulk of my time providing food, cell phone, education, housing, medical care, petty cash and in state college tuition for the 39,000,000 illegal aliens that are permanently vacationing in my country.

The statement that tuning between centers is not always as accurate as indicating off a tight fitting bore - rod is true.

However remember that the idea here is to have clearance inside the muzzle devise, be it a recoil reducer or a can.

So if you can indicate to zero tolerance on the bore, or get within .001" on centers ( a good lathe set up right will be under .001" many times) and then you cut the inside of the device at least .020" oversize, how would being more centered by .0005 to .001" make any difference at all?

It doesn't.

Some have speculate that the larger clearance on one side can compress the gas enough to off-set a bullet, but the Military's in the USA as well as the Germans the Austrians and the Swiss have disproved this.