Muzzle break threading 300 win mag

[J E Custom]

I found a video on youtube of a guy running gauge pins in the muzzle with 5/8" and 3/4" threads. His point was that the 5/8" thread removes too much material and causes the bore to expand whereas the 3/4" leave enough material to prevent this.

This seem to me that a brake should be torqued down to eliminate the bore expansion. Any thoughts on that? Torque recommendations?

It is not so much the thread size, but the bore size compared to the thread size picked, and the thread fit. Torque should be no more than 30 inch/pounds.

If the thread fit is not good and the barrel tenon is to thin it can certainly compress the bore when tightened.

The barrel thread should not expand if the barrel has been properly heat treated and is not to thin that allows the tenon to expand when fired.

I recommend the largest thread size that the barrel muzzle can take and still have about 1/16'' shoulder to seat on. This is not always possible but it helps.

Thread fit and quality is very important, and thread Minor Diameter to bore thickness also. I believe that .150 minimum barrel wall thickness is ok as long as everything else is done correctly and the brake is not over torqued.

So if the proper thread size is used to give more that .150 barrel wall thickness and the barrel bore
expands, the barrel was not properly stress relieved. If the threads were not a good fit and the wall thickness was less than the recommended .150 and then it is over torqued, it could certainly reduce the bore diameter and also become subject to a catastrophic failure at worst, and effect the accuracy at best.

A "properly" installed muzzle brake has never hurt accuracy to my knowledge and in many cases improved accuracy.

J E CUSTOM

 

[Roeder]

I even found posts from some guy named Dave Tooley stating he installs 1/2-28 in .308 rifles regularly. I don't know him but I have used some stocks that are named after him. He mentioned that even if it does fail there is no danger to the shooter. He stated that he has seen all sort of brake failures from botched jobs and at worst the brake flies harmlessly down range.

FWIW Dave Tooley is one of the most accomplished and respected rifle builders in the country and fits more barrels in a year than most guys do in a lifetime.

 

[J E Custom]

I even found posts from some guy named Dave Tooley stating he installs 1/2-28 in .308 rifles regularly. I don't know him but I have used some stocks that are named after him. He mentioned that even if it does fail there is no danger to the shooter. He stated that he has seen all sort of brake failures from botched jobs and at worst the brake flies harmlessly down range.

FWIW Dave Tooley is one of the most accomplished and respected rifle builders in the country and fits more barrels in a year than most guys do in a lifetime.

Go for it !!!! And witness a failure first hand and tell us if it hurts. At best you will have to change your drawers. and the fact that anyone would say. "Even if it does fail, there is no danger to the shooter" would make me wonder, and what about bystanders ?

I have stated many times, just because many people do something and get away with it because they know a guy that has an uncle that read about this expert doing it, so it must be OK.

I don't think that I am smarter or wiser than anyone else, I just refuse to do things that are marginal and have the possibility of catastrophic failure. Also It doesn't matter how many barrels a person fits, It only takes one failure to learn a valuable lesson.

Do What you want, and live with your decision.

J E CUSTOM

 

[Roeder]

I should know better than to wade into this discussion again. It occurs to me that the dozens or hundreds of capable smiths and manufacturers that have manufactured and fitted thousands of brakes with "MARGINAL" thread sizes may not have been stupid or foolish or ignorant. They may have even have engineering degrees and had taken the time to make the rather simple calculations of tensile strength for those weak, skimpy threads. Long before todays huge, heavy, and very effective brakes came along, the typical brake installed on a lightweight sporter rifle was small, 1 1/2 to 2 1/2 inches long and finished at barrel diameter. Those brakes were installed with the 1/2-32 or 1/2-28 threads on up to 30 caliber without issue. Todays large diameter oversize brakes are much more effective than the small ones, but they also impart a lot of load to the attachment threads. The decision on what minimum thread size is acceptable should take all factors into account including barrel length and diameter, cartridge size and barrel pressure at bullet exit, and the size and mass of the brake.

The .150 minimum barrel wall thickness spec. for fluting barrels takes different factors into account, primarily the fact that flutes running the length of the barrel create a weakness that would result in an extremely dangerous condition in the event of a rupture that could release high pressure gasses and spall toward the shooter or bystanders. The burst strength required at the last .600 inches or so of barrel at the muzzle is not subject to the same conditions or risks. There are countless examples of factory designs of both military and civilian barrels that employ muzzle threads that have considerably less than .150 wall thickness.

Obviously, every gunsmith has to decide for himself what he can do safely without exposing himself to excessive liability. What is right for you and the brakes you design, sell. and install may be different from other situations and designs.

 

[J E Custom]

Don.t apologies, this is just a discussion.

I am basing my Opinions on seeing many failures and repairing many of them. As mentioned earlier By a very good and known gunsmith and all of the master gunsmiths that taught me that .150 was the minimum thickness allowed to be infringed upon the barrel wall even when drilling and taping sights. This is a very small area and it is plugged by the screw.

I just want to keep people out of trouble by passing on my experience, Not my opinion as a gunsmith and hope they head the warning. I have learned by the mistakes of others and continue to learn, so the same thing doesn't happen to me or others with one of my rifles.

I have also known several gunsmiths that had catastrophic failures and later said they knew better
but did what the client wanted. Fortunately the firearms failed when they tested them and the client was not hurt. I learned from them not to take short cuts, do anything marginal, and simply refuse to do work that could be unsafe.

Under ideal conditions some practices are marginally safe, But is anything changes, bad things happen. so why not have some safety margin for those situations.

J E CUSTOM

 

[TwoMore]

Don.t apologies, this is just a discussion.

I am basing my Opinions on seeing many failures and repairing many of them. As mentioned earlier By a very good and known gunsmith and all of the master gunsmiths that taught me that .150 was the minimum thickness allowed to be infringed upon the barrel wall even when drilling and taping sights. This is a very small area and it is plugged by the screw.

I just want to keep people out of trouble by passing on my experience, Not my opinion as a gunsmith and hope they head the warning. I have learned by the mistakes of others and continue to learn, so the same thing doesn't happen to me or others with one of my rifles.

I have also known several gunsmiths that had catastrophic failures and later said they knew better
but did what the client wanted. Fortunately the firearms failed when they tested them and the client was not hurt. I learned from them not to take short cuts, do anything marginal, and simply refuse to do work that could be unsafe.

Under ideal conditions some practices are marginally safe, But is anything changes, bad things happen. so why not have some safety margin for those situations.

J E CUSTOM

There are alot of guys like me who are not quite that experienced and read these posts , very good stuff. I for one appreciate the knowledge and really want to be safe. Thanx

 

[J E Custom]

There are alot of guys like me who are not quite that experienced and read these posts , very good stuff. I for one appreciate the knowledge and really want to be safe. Thanx

You are welcome !!

All I can hope for is that My experience will keep someone from getting hurt.

J E CUSTOM

 

[eklarsen]

Yes, it is fine

 

[Gord0]

Just read through the whole post and this is why I like this site. People having a conversation and disagreement without acting childish.
I'm not a gunsmith, just like to tinker. I am an engineer, and also a machinist in the aerospace industry. I deal with threads, a lot of threads. I've learned more about threads and thread failure than I've ever wanted to. Depending on the tool used to make the threads there can be massive differences in strength with the same thread size. Cut threads with a very sharp point single point tool and you have a stress point at the root. Add a small radius to the point and you have a much stronger thread. And possibly a different thread spec. Cut it with a die and get a completely different result, thread whirl it and yet another. The way the brake fits is another factor. The type and way the barrel was rifled will also play a role in the end strength too. Standard rifling that is cut vs button, vs 5r, vs 5c will all have different strength against bursting. There are so many factors in play that you would have to model every single thing and do FEA to see if you are in a good safety margin. I would guess that most gunsmiths don't have access to this. Something that a major barrel maker would. I agree with J.E. on this one.