barrel diameters and muzzle brakes.

[J E Custom]

In an earlier post I stated I had repaired barrels that had shot the brake off for one reason or the other. (That is one of the reasons).

Just because "some" others have not had a problem doesn't mean I want to do it.

Muzzle brakes are a relatively new addition to rifles (I personally did not like or use them until
a few years ago when I realized the advantages they offered) Most rifles over 10 to 15 years old
do not have provisions for threading the barrels because they were not designed to attach anything to the muzzle, so barrel wall design thickness was based on finished barrel thickness.

A site sponsor that is one of the best gunsmiths, mentioned to me that he remembers while going to Gunsmith school he was told 'when drilling and taping site base holes in barrels never to go deeper than necessary and to leave .150 thousandths of barrel from the bore to the bottom of the drilled hole.

I looked in some of my gun Smithing books and they recommended the same thing.

I worry about the do it your self people that do not know there are minimums and could get into trouble. The gun smiths should take care of things like this (That's why you hire them).

As we are more and more into tactical firearms you will notice that none of the .308s have 1/2x28
threads (Most are 5/8x24) the , .223s still use the 1/2x28 because they can.

J E CUSTOM

 

[Hired Gun]

I have seen a lot of rifles use 1/2 inch brakes. Anyone ever have a confirmed problem with a. 308 cal brake with a 1/2 dim thread that the root cause was a thin wall!

I do a couple a week in 1/2-28. I use 9/16-24 when I can but many people do not like the look of the fat brake that goes with it. I would say hands down our most popular installation. Rem or Win sporters in 300 RUM. Followed by those skinny barreled Rugers in 7mm and 300 Win mag. It used to concern me but they have stood the test of time.

 

[winmag]

This is another excellent info and should be on the "sticky".

Agreed!

 

[royinidaho]

Rhian,

It's been ages since my navy metallurgy training.

IIRC the term is nil ductility transition point. That beyond which plastic deformation occurs.

Just though I'm chime in. . .

 

[CHARLIEDUECE65]

So what is the minimum break wall thickness. I have a factory rem 30 cal barrel with a .644 muzzle. I bought a harrels break with a .750 od/9/16x32 thread. Will it be safe to contour this brake to the muzzle contour or close to it? I realize the walls are going to be really thin. Thanks

 

[J E Custom]

So what is the minimum break wall thickness. I have a factory rem 30 cal barrel with a .644 muzzle. I bought a harrels break with a .750 od/9/16x32 thread. Will it be safe to contour this brake to the muzzle contour or close to it? I realize the walls are going to be really thin. Thanks

Based on my conversations with barrel makers and engineers I made a simple guideline for tenon and thread size. it is based on .150 minimum barrel wall thickness between the minor diameter
of the threads and the rifle bore.

This minimum thickness is what the barrel makers use to flute a barrel, The thinnest number they gave me was .137 (depending on cartridge pressure and bullet diameter to) .150 thousandths.so
in order to error on the side of caution it did my calculations based on .150 thousandth wall.

A simple way to figure it is to take the bullet diameter, and add .300 thousandths. that will give you the Recommended barrel diameter for installing a thread for the brake. (Different thread pitches have different minor diameters but the .150 should cover it as long as you have enough barrel left over to have a shoulder to seat the brake against.

Hear is a link that may help.

www.jecustom.com - FAQ's

J E CUSTOM

 

[Clark]

Here is a pic of my father working on this gun patent:
Patent US3894471 - Rapid fire weapon for turret installation - Google Patents

I asked him how to calculate the max pressure in a gun [for my 45/70 handi rifle]
He showed me Lame's formula in a textbook for thick walled cylinders, that Lame figured out 500 yeas ago:
Stress for Thick Walled Cylinders using Lamé

Cylinder stress - Wikipedia, the free encyclopedia
Then he said that thin walled hoop stress was
Stress in the steel = [pressure][inside diameter]/[2][wall thickness]

I asked him where he got that.
He shouted in my face, "BY INSPECTION!"

I was late the the party, but I guess if someone has to tell you how to calculate thin wall hoop stress, you are stupid.

 

[CHARLIEDUECE65]

Ok, I talked to harrels and they said if I leave the break .025 over my barrel diameter I should be OK with my given dimensions . They did however recommend to back taper it and leave the break bigger for the break to work better.

 

[bigngreen]

So what is the minimum break wall thickness. I have a factory rem 30 cal barrel with a .644 muzzle. I bought a harrels break with a .750 od/9/16x32 thread. Will it be safe to contour this brake to the muzzle contour or close to it? I realize the walls are going to be really thin. Thanks

I've turned that brake down to .712 and that was about as thin as I would take it, functions well, looks good.

 

[J E Custom]

When I posted this thread, it was to help those that did not know if they could install a brake
safely on there rifle. It is not intended to be come a SAMME standard, It is just a guideline.

All "Good" firearms have a built in safety factor (Normally 50%+). I am sure you could get by with less BUT WHY ?

I am having trouble understanding why anyone would want to reduce the barrel below a well
known safe thickness and risk a catastrophic failure. The fact that It has been done, doesn't
mean it wont fail when used in another application.

If you bought a rifle with a skinny barrel that should not be threaded for a muzzle brake, so be it.
it happens and we move on. Some times You have to change barrels.

Almost all rifle makers 20 years ago did not have muzzles brakes in mind when they designed their
firearms because everyone wanted lite and sleek.now that muzzle brakes are more popular some even come with them and the manufactures are offering heavy barrels.

Times have changed and I for one have to make myself adapt to these changes to stay safe. with the new cartridges and pressures I don't have to calculate hoop strength, because there are to many variables that can make the calculations dangerous if you go by the minimum thickness "REQUIRED" .

I For one don't care if someone else does it, if I don't believe it is safe, I wont do it. I once knew a
very good gunsmith that practiced the "It will be fine theory" He blew up several rifles bad enough to knock him out. I though the world of him but would not let him work on any of my rifles because
of his good enough philosophy.

The fact that I wont do something doesn't mean it cant be done, It just means that I am uncomfortable with it so I wont do it.

I hope the post helped some.

J E CUSTOM

 

[FEENIX]

Ok, I talked to harrels and they said if I leave the break .025 over my barrel diameter I should be OK with my given dimensions . They did however recommend to back taper it and leave the break bigger for the break to work better.

I purchased the rifle in the picture in 1991 and has a magnum sporter barrel (.600" at the muzzle) and have a muzzle brake installed in 2003. The muzzle brake is a Holland [FONT=verdana,arial][FONT=Verdana, Arial][FONT=Verdana, Arial, Helvetica][FONT=Arial,Helvetica][SIZE=-1]QD Brake (S/S - 9/16 ins. - 28 TPI - .580 -.650 tapered)[/FONT][/FONT][/FONT][/SIZE][/FONT] and installed by Dave Young in Sand Coulee, MT ... some of you here know him and he has built some awesome LR rifles. I probably have ~ 1000 rounds through since the muzzle brake installation without any issues.