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Anything really wrong with sanding the back end of a non self timing brake until it’s timed properly? I plan on using wet/dry sand paper over a sheet of glass. How real a chance do I stand of screwing up concentricity if I go this route? Seems like a better option than shims or crush washers, right? Talk me into or out of this plan.

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I don't think it is the concentricity that will be affected, there is a high probability that you may end up with the shoulder not being square with the bore/threads


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Originally Posted by Jkob
I don't think it is the concentricity that will be affected, there is a high probability that you may end up with the shoulder not being square with the bore/threads
That...


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It’s always a better option to wing it than use the conventional method.


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why not sand the crush washer

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Originally Posted by SDHNTR
Anything really wrong with sanding the back end of a non self timing brake until it’s timed properly? I plan on using wet/dry sand paper over a sheet of glass. How real a chance do I stand of screwing up concentricity if I go this route? Seems like a better option than shims or crush washers, right? Talk me into or out of this plan.

I've done that before and had no problems. Fine wet/dry over a smooth granite tile. Just be careful to go slow and use even pressure, rotating the brake between strokes.


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Originally Posted by steveredd1
why not sand the crush washer
Because some seem to think that using a crush washer at all is a bad idea.

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Originally Posted by Jkob
I don't think it is the concentricity that will be affected, there is a high probability that you may end up with the shoulder not being square with the bore/threads
Well, that’s kinda what I meant. I guess a better question is could shoulders that aren’t square then cause non - concentricity to the bore?

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Originally Posted by JPro
Originally Posted by SDHNTR
Anything really wrong with sanding the back end of a non self timing brake until it’s timed properly? I plan on using wet/dry sand paper over a sheet of glass. How real a chance do I stand of screwing up concentricity if I go this route? Seems like a better option than shims or crush washers, right? Talk me into or out of this plan.

I've done that before and had no problems. Fine wet/dry over a smooth granite tile. Just be careful to go slow and use even pressure, rotating the brake between strokes.

Yes, I was also planning to sharpie the back end to track progress and to keep it square.

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How much material do you need to remove to get it in time? I wouldn’t hesitate for a few thousandths (.005-.008) but I don’t have the patience to do it that way for .020”.

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If a brake is installed properly it is done with the barrel in the lathe and it should have been timed then. Plus, the bore of the brake should be bored to proper diameter while in the lathe so it is centered with the bore. There's more to it than just buying a brake and screw it on.

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why not use shim washers


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Originally Posted by WayneShaw
If a brake is installed properly it is done with the barrel in the lathe and it should have been timed then. Plus, the bore of the brake should be bored to proper diameter while in the lathe so it is centered with the bore. There's more to it than just buying a brake and screw it on.

Hence my question. Seems to be split opinions on this. Some folks think that no matter what the installation method, screwing a brake on after the fact is a bad idea. And others, some I know personally, have done it without any issues at all. Confusing. Perhaps I should stick with a self timing brake so I can just screw it on and not worry about it. Just hate the look!

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Originally Posted by SDHNTR
I guess a better question is could shoulders that aren’t square then cause non - concentricity to the bore?

Yep. -Al


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I have lapped extreme low tolerance hydraulic pump and valve flat face components for years, and marine diesel fuel injector valves using a quality mirror as a lapping plate and 3M emery paper, I'd bet there is a Youtube video on the figure eight motion required.


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So why is this alignment to the bore not an issue with self timing brakes? Everybody just screws those on without a second thought. Is the hole drilled out sufficiently larger than bore diameter to allow for tolerance stacking on a self timer and not a permanent brake? If yes, why couldn’t non-self timing brakes also be bored out to do the same thing? Why do we treat these differently?

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Originally Posted by SDHNTR
So why is this alignment to the bore not an issue with self timing brakes? Everybody just screws those on without a second thought.

As Wayne noted, the best performing precision brakes have the bore no more than .020-.025 over the barrel bore diameter and the end hole will be perfectly concentric to the bore. By design, 'self timing' brakes need to have more clearance to allow for misalignment. The tradeoff is performance (accuracy). If that's not as big of a deal, a self timing brake will still 'brake' effectively.


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Originally Posted by Al_Nyhus
Originally Posted by SDHNTR
So why is this alignment to the bore not an issue with self timing brakes? Everybody just screws those on without a second thought.

As Wayne noted, the best performing precision brakes have the bore no more than .020-.025 over the barrel bore diameter and the end hole will be perfectly concentric to the bore. By design, 'self timing' brakes need to have more clearance to allow for misalignment. The tradeoff is performance (accuracy). If that's not as big of a deal, a self timing brake will still 'brake' effectively.

Thanks. Exactly what I thought.

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If the thread are cut concentric to the bore of the rifle, and the threads on the brake were cut concentric to the bore of the brake, (as both should have been) then the threads are what is keeping everything aligned.
By sanding or not having the back of the brake square to the shoulder on the barrel, you can cause misalignment of the bore of the brake only to the amount of clearance in the threads, BUT the longer the brake is, the more it will show up.
The rule of thumb is, .017 per inch per degree. In other words, is your brake were out of alignment 1 degree from the center line of the bore of both the barrel and the brake, and the brake was 2" long, it would be out by .034" (.017x2=.034")


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Yep...the math doesn't lie.

A good friend built a customer a very good 6.5x284 hunting rifle....shot great. A couple months later, the customer calls all upset because it's shooting 10" groups at 200.

The customer brings the rifle back for a look see and surprise, surprise...it has a self timing brake on it that wasn't fitted when my friend did the build. Turns out the customer had someone else thread the muzzle and install it.

Looking at it, the copper wash from the bullet striking the inside of the exit hole at the end of the brake was obvious.

He removed the brake, walked outside to his range and rapped off a sub 1" group at 200.


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