The Home Machinist!

Hi,

Is there any standard to the indexing of the thread on the end of a muzzle so a muzzle brake will index correctly?

Thanks

Nope. There really would be no way to do it if all parts weren't done on the same CNC machine.
Usually compression washers or peel washers are used to align the brake. When I am making brakes I thread the barrel abd screw the brake on for index before I machine the slots in the brake.

Same way you index a barrel. Divide the TPI into 1.

Screw on the brake, measure how many degrees it needs to turn, say 20 degrees will line you up, and then if you are using 18 TPI, divide 18 into 1 = 0.055” per 360 degrees turn. Divide 0.055 by 360 gives inches per degree (this will be a real small number!) that the brake will need to move. Then 20 times that number gives you how much to take off the face to move the brake 20 degrees, ie 0.003”

catskin wrote:Same way you index a barrel. Divide the TPI into 1.

Screw on the brake, measure how many degrees it needs to turn, say 20 degrees will line you up, and then if you are using 18 TPI, divide 18 into 1 = 0.055” per 360 degrees turn. Divide 0.055 by 360 gives inches per degree (this will be a real small number!) that the brake will need to move. Then 20 times that number gives you how much to take off the face to move the brake 20 degrees, ie 0.003”

Hi thanks but that wasnt what I was asking, I realize taking a skim off the brake will line it up but I was asking if there was any standard to where the thread ends on a rifle barrel. so if Mr smith down the road had a rifle with a 1/2 20tpi thread on the front I could make him a brake that would index correctly without checking his thread.

Thanks

That has to be an interesting problem to figure out. I would think it would be easiest to include a small sampling of washers to change the bottom seating distance, but even that isn't foolproof.
David from jax

No there is no standard. I use .500x28 tpi for hunting tapered barrels and .625x24 for varmint weight and sometimes .750x 20 for the large stuff. All are custom fit for each break. I index them by skimming as you put it. Divide the thread by 1. I install about 20 a year on hunting rifles.

Blagg Rifles

I used the formula that catskin supplied to line up a home-brew muzzlebrake for my AR15, it worked great. ( The formula )

http://i239.photobucket.com/albums/ff20 ... G_1011.jpg

http://i239.photobucket.com/albums/ff20 ... G_1035.jpg

http://i239.photobucket.com/albums/ff20 ... G_1039.jpg

While the pitch math will give you an idea, cut conservatively and check the position. If you calculate .020" to cut, take .010 and test fit it. Torque the brake with a strap wrench (or appropriate wrench) and see where it indexes. Once I get to within 1 thou (or more depending on how your machine cuts), lap the end of the brake on a flat surface with 400 through 1200 grit to finish the index.

I have discovered a good way to create index marks at work that is better than the eye- level the assembled rifle with the barrel installed and torqued. A rubber-jawed vise is useful here. Scribble a mark at the top center behind the muzzle (if threading, obviously don't mark metal that will be removed) and then rub the mark with the level, holding the bubble centered. You will end up with a fine rub mark in the wet ink that is tangent to top dead center. If you mark the muzzle brake/flash-hider at TDC you will have a very clear index to reach.

Colt-made AR-15s, and presumably M-16s also, having the type "birdcage" with slots only on top, used a shim stack to obtain tight-orientation of the screwed-on part.

CB&Q