Muzzle break threading 300 win mag

[bobcat trapper]

Is 1/2x28 enough for a pencil barreled 300 win mag? My initial though is no but not 100% on it?

 

[ShtrRdy]

I would sure see if you could do 5/8-24

 

[FEENIX]

Is 1/2x28 enough for a pencil barreled 300 win mag? My initial though is no but not 100% on it?

For what it is worth, I have a Holland's [SIZE=-1]QD muzzle brake S/S - 1/2 ins. - 28 TPI -.530 -.575 tapered[/SIZE] (item# 12-3075-SS-T) on my Savage 111F .300 Win Mag with .625" OD IIRC at the muzzle since 2003 without any issues.

 

[Georgiashooter]

I would personally want to go 9/16-24 or 9/16-32, depending on the brake you're using and the exact diameter of your barrel. Getting thin with 1/2-28. Probably won't hurt anything as feenix has shown, just like as much meat up there as possible!!

 

[bobcat trapper]

I'm with everyone on the more meat there the better I was asked if I could put a break on a mountain rifle with a #1 contour barrel and 1/2-28 is about all I can get.

 

[shortgrass]

Just exactly how big (or small) is a "pencil barrel" at the muzzle?

 

[bobcat trapper]

.525 or .575 if I loose a few inches might be the better route.

 

[J E Custom]

What you are looking for is a minimum barrel wall thickness after threads are cut (Minor Diameter)of .150 (On cartridges that are less intense you can safely drop to .125 minimum.

Some of the older rifles and the light contoured barrels were never intended to have a muzzle brake installed and are already near the minimum wall thickness.

The simple formula for calculating this is = Barrel diameter at the muzzle , minus bore diameter, Divided by two. if the minor thread diameter does not reduce the thickness below the minimum, it will be ok.

On my web site I have included a brief description of the requirements of different calibers that may help.

www.jecustom.com - FAQ's

J E CUSTOM

 

[FEENIX]

.525 or .575 if I loose a few inches might be the better route.

Extracted from https://www.hollandguns.com/ ...

 

[Hired Gun]

We have done near 100 .308 sporter barrels with 1/2-28 brakes if that's all that will fit. There is one well known maker of lightweight rifles that regularly installs 7/16" brake thread on their 300 RUM LW rifles.

The brake strengthens the barrel as long as you don't go cutting a thread relief on the barrel. The brake acts like an band of extra material around the threads. Just don't tighten it down real hard or it will put a choke in the bore under the threads. Test it with a tight bushing before and after the installation.
Knowing that a 500 S&W revolver barrel (shown) is only .718" major o.d. over the threads minus the thread depth can contain 60,000 psi right at the frame and is proof tested to 50% overpressure is comforting when no rifle made has 1/4 that pressure at the muzzle. Dan Wesson barrels are even thinner.

Most importantly don't be shortening a customers barrel without consent. A 300 WM is not really a 300WM at 24". It's more like a 30-06. At 22" it's a bit more than a 308Win. Just saying if you do cut one without consent you would be expected to replace the barrel at your expense.

 

[J E Custom]

Just a word of caution. when I started making custom brakes I was curious about minimum safe wall thickness of barrels after threading, and talked to many barrel makers and there engineers,

The numbers varied from .137 thousandths to .150 thousandths Safe minimum at the muzzle.
(.013 thousandths difference between all of there recommendations).

If you look at a 1/2" 28 thread on a .308, this is what you have for a wall thickness.

Minor diameter of a 1/2 28 thread is .0219 + or - depending on the quality of the threads
- .500 major diameter of 1/2 '' 28 = .486 minus the .308 bore diameter = .181 divided by
2 equals .090 wall thickness. (Almost 1/2 of the recommended wall thickness).

Comments:
There is normally .002 thousandths clearance between the major diameter of threads and the minor
diameter in order to fit properly. So I don't want to rely on the brake to support the barrel threads.
many thread fits are much worse than that But even if we assume they are the best it still does not
truly support the barrel threads unless you use some kind of thread filler that hardens to fill the space in the threads.

Most manufactures have gone to 5/8 24 threads for .308 bores and feel it is a safe thread diameter.
It also helps to prevent the phenomena of bore diameter changes when tightening the brake.

lots of older rifles and ultra light rifles have barrels that were never intended for brakes and the barrels are to small for a threaded brake. this is case for the clamp on brakes to be used.

I have seen brakes shot off the barrel and have repaired some of them and in many cases the person or smith could have used a larger thread diameter.

I can only warn people that just because it has been done, doesn't mean it is safe because there are so many variables.

So, If a person can live with a wall thickness of .090 thousandths, then the 1/2'' threads on a .308
may be ok as long as everything is good and the barrel material will support this wall thickness, but I will not depend on it and prefer to go by the recommendations of people that build barrels and know the material strength.

This is just My opinion and not intended to start an argument.

J E CUSTOM

 

[Hired Gun]

I'm not going along just because a few guys got away with it. I'm saying major firearms manufacturers are designing and building guns for mass consumption that push these 'limits".

JE, What do you think about S&W using barrels of about .109" thick on the 500 S&W rated for everyday use at 60,000 PSI and Dan Wesson using barrels .500" diameter for the .357 Magnum at 35,000psi? The proof loads for these guns are rated at 50% over these figures. How much pressure do you think a 300 RUM left in the barrel when the bullet is at the very end of the barrel?

I don't know the exact pressure either but I have bobbed a number of them with a slight bulge from firing a slug of mud out of them. Not one was ever split. As far as support from the brake threads as long as the brake has any tension at all the v portion of the threads in the brake is firmly contacting the corresponding v form from the barrel. It doesn't need filled solid to gain support.

I have a Rifles Inc 300 RUM in my shop right now that had a 7/16-28 brake on it and I was just reminded that Kimber Mountain Ascent rifles use 7/16-28 threads on their 30 cal rifles.

Here is the math on these popular revolvers. I'm guessing somebody of at least one of these companies consulted an engineer before pouring millions into making these firearms.
.718" -.500" = .109" is capable of regular use at 60,000psi
.500" - .357 = .0715" is capable of regular use at 35,000psi.

I have also noticed a lot of semi automatic high powered pistols that have very thin barrels that operate at 37,500 to 40,000 psi. Then there are the fluted cylinders on these revolvers. Many of which get down to less than .100 thick. I have also brought it up with the owners of several barrel makers and I doubt any of them are engineers but they have no problem fluting barrels down pretty thin. They frequently say the pressure curve drops of dramatically after a few inches down the barrel. I worry a lot more about the guys asking for the chamber shank be reduced right at the lug to as small as possible leaving the chamber with not much thickness right at the throat. I have yet to do it due to crazy cost of the Proof research barrels but I suspect they are very thin under that epoxied on carbon sleeve. Especially on the .375 CheyTac barrels.

I have a Dan Wesson .357 barrel with Eleven 158 grain jacketed soft point bullets in it and it only bulged to .513" right outside the frame. Of course my word means nothing here so I'll let the picture do the talking. It's the best conversation starter of all my wall of shame examples.

 

[Edd]

I recently ordered a Bartlein custom Palma style contour .338 barrel with deep flutes. They required me to get a contour size that would have a minimum thickness of .170" under the flute at the muzzle end.

 

[Pdvdh]

Then there are the fluted cylinders on these revolvers.

I don't know about the rest of the examples, but revolver cylinders could very well be made of a stronger grade of steel, compared to pistol/rifle barrels. No one has to install internal rifling on those cylinders.