Muzzle break threading 300 win mag

[J E Custom]

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.

I hear everything you are saying and agree that these things do exist. as far as the pressure at the muzzle of a rifle or pistol It is normally somewhere between 10,000 to 17,000 psi at the muzzle,

Chamber pressure is much higher and this is where the SAMMI pressure specification is set. on revolvers it is normally lower because of the gas loss between the cylinder and the barrel. Most revolvers fail at the cylinder from the max pressure. The fluted cylinders normally have the flutes between the cylinder bores so as not to weaken the cylinder. Most shotguns fail just in front of the receiver where there is no extra support. Rifles generally fail near the muzzle (About 2/3 rds from the action and continue to the muzzle. If the barrel splits soon enough and can relieve most of the pressure,
a muzzle device can sometimes stop the barrel from splitting all the way, but often as not it just shoots the brake off if the barrel wall is two thin.

Here is a link to some barrel failures that proves that it does happen and can be prevented.

https://www.google.com/search?q=rif...4eYCw#imgrc=yQ5P6r7G5K3djM:&spf=1495079543300

I was worried about wall thickness when I found a rifle that had a bulge in the bore of only .004 to .006 thousandths about 8'' from the muzzle. You could not see it but while cleaning it you could feel the patch get loose and then tight again. It was a fluted barrel that the flutes were two deep and did/could not support the pressure. I replaced the barrel with a non fluted barrel and later decided to cross section the barrel, the web between the bottom of the flutes and the bore was less that .100 thousandths. (Of course the pressure would be higher at this point but the failure occurred anyway.

I have seen many of these failures but never had one of my weapons fail except for the one mentioned, and I considered it was caused by a very bad fluting job and for many years I would not own a fluted barrel because of it. Once I talked to the favorite barrel maker he convinced me that proper fluting was not the problem but poor fluting and not enough wall thickness. (This is why most barrel makers will not flute or warranty fluting on a barrel below a certain contour because of the wall thickness issue.

I am probably to conservative but It has served me well and I don't want to be one of those shooters in the link that found out the hard way. or find out that some of the work that I performed failed and possibly hurt someone.

Over the years I have declined to do something that I though was marginal because of my concern
with it and to date have a 100% clean record from failures, and will stick with my philosophy. Why take a chance, Murphy is always out there and ready to pounce.

Just My Opinion

J E CUSTOM

 

[J E Custom]

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.


Please tell me that this is a Typo, or tell me the name of the well known rifle maker that regularly
in stalls 7/16'' brakes on 300 RUMS.

This would leave the barrel wall .028 thick and would be very dangerous, especially on something as powerful as the 300 RUM.

J E CUSTOM

 

[Hired Gun]

Fourth paragraph of my previous post.

Here is a link to the Kimber brake. Terminator also makes the T-1 brake for .308 with 7/16-28 threads. On their page they have a video of the T-1 in use on a 300RUM.

Adirondack Muzzle Brake - .308 Win. - Accessories - Sporter Rifles - Rifles

T1 Brake - Terminator Products


Rifles Inc does it regularly on their ultra light 300 RUM rifles. If I beat the brush I'm sure I could find more than a few more ultra light rifle builders that use 7/16-28 over .308.

I draw the line there. I will never put a 7/16 thread brake on a .308 bore. The only reason I brought it up was if they can do 7/16-28 over a .308 then a 1/2-28 should never be a problem. 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.

I believe a lot of it has to do with who "fit" the threads verses a guy that just cuts threads and if they need to use a thread relief. Ours are compared to micrometer spindle threads. They are not .001 deeper than needed and we never use a thread relief on outside threads.

The number of 1/2-28 over .308 bore we do grows weekly. I know I'm not the only one. Ask any major brake maker. Doing this full time as my sole occupation for over 8 years now and not one comeback. My mentors were famous long before the internet and they have no issues with doing it either. Additionally, universally everyone has commented the rifles shoot dramatically better after our brake and crown job.

Now that I think of it you are the only one I remember saying it is unsafe or saying you have seen failures. I would like to hear more about those.

 

[J E Custom]

Fourth paragraph of my previous post.

Here is a link to the Kimber brake. Terminator also makes the T-1 brake for .308 with 7/16-28 threads. On their page they have a video of the T-1 in use on a 300RUM.

Adirondack Muzzle Brake - .308 Win. - Accessories - Sporter Rifles - Rifles

T1 Brake - Terminator Products


Rifles Inc does it regularly on their ultra light 300 RUM rifles. If I beat the brush I'm sure I could find more than a few more ultra light rifle builders that use 7/16-28 over .308.

I draw the line there. I will never put a 7/16 thread brake on a .308 bore. The only reason I brought it up was if they can do 7/16-28 over a .308 then a 1/2-28 should never be a problem. 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.

I believe a lot of it has to do with who "fit" the threads verses a guy that just cuts threads and if they need to use a thread relief. Ours are compared to micrometer spindle threads. They are not .001 deeper than needed and we never use a thread relief on outside threads.

The number of 1/2-28 over .308 bore we do grows weekly. I know I'm not the only one. Ask any major brake maker. Doing this full time as my sole occupation for over 8 years now and not one comeback. My mentors were famous long before the internet and they have no issues with doing it either. Additionally, universally everyone has commented the rifles shoot dramatically better after our brake and crown job.

Now that I think of it you are the only one I remember saying it is unsafe or saying you have seen failures. I would like to hear more about those.

No Problem.

A long time ago I wouldn't use a muzzle brake for the same reason as most, Noise. But I got older, and decided to save the remaining hearing I had and started hunting with hearing protection it dawned on me that some of the rifles could/should have muzzle brakes installed on them.

I did the normal uninformed thing and bought commercial muzzle brakes. When I saw the first AR 10
in 308 the 1/2'' threads looked small for the 308 bore. The AR 15s in 223 looked fine. and I "Assumed" they were ok. Then when the AR 10s started getting and more people were marketing them I noticed that Most had switched to 5/8 24 for the 30 cal. Still not sure if I was just being conservative I decided to do some research and talked to the barrel makers about there limits and the reason for there limits.

Without rehashing previous post it all boiled down to safe barrel wall thickness. One of my concerns
is the fact that this group of shooters are notorious for pushing the envelope and with an already marginal thickness only bad things can happen.

I personally want more than .072 barrel wall on a 30 cal (1/2 28) and to go to a wall thickness of.028 (7/16 tpi) is scary.

I believe that the 1/2 28 has been used for 30 caliber but when engineers that work for the barrel makers stated that a minimum barrel wall was .137 to .150 I have to believe them. I also will not hesitate to tell someone that I will not infringe on this wall thickness and do something that I feel is marginal at best.

You can do as you please and others can/will I am sure but the warning is still there. I don't do this for a living so I am not managed by profits just quality and if I can save just one shooter the experience of having a rifle fail because it was more convenient to do something marginal I will.

Do what you like, but just think about a barrel with a wall thickness twice the thickness of your brass
and you will decide on your own what is best and live with your decision.

J E CUSTOM

 

[Hired Gun]

So no first hand or any experience with failed brakes due to insufficient wall thickness? Do you have any examples at all?

Your calculations are not taking all aspects into consideration and it's clear you lend no credibility to my experience, knowledge or any of the number of factual evidence I have provided so that's it for me.

The OP asked the people of this forum if it was safe to use a 1/2"-28 thread brake over a .308 bore. In my opinion which is shared by the vast majority of gunsmiths that I know believe 1/2"-28 over a .308 barrel though not ideal is perfectly safe. I would also add that when doing this task find a smith that doesn't need to thread with a relief. As much metal as possible should be retained on the barrel as possible.

I've go a back log to work on.

 

[J E Custom]

So no first hand or any experience with failed brakes due to insufficient wall thickness? Do you have any examples at all?

Your calculations are not taking all aspects into consideration and it's clear you lend no credibility to my experience, knowledge or any of the number of factual evidence I have provided so that's it for me.

The OP asked the people of this forum if it was safe to use a 1/2"-28 thread brake over a .308 bore. In my opinion which is shared by the vast majority of gunsmiths that I know believe 1/2"-28 over a .308 barrel though not ideal is perfectly safe. I would also add that when doing this task find a smith that doesn't need to thread with a relief. As much metal as possible should be retained on the barrel as possible.

I've go a back log to work on.

Sorry I couldn't convince you that what you are doing is very risky so I wont try anymore. And if you read all of the post I have had first hand experience with repairing them, just not to the rifles that I have personally installed brakes on. I have also shown many examples of failures of many different types that for one reason or another they failed and some injured people. I just don't by in to the notion that "IT"S GOOD ENOUGH EVEN THOUGH IT"S NOT IDEAL"

Lots of manufactures, and some gunsmiths tend to blame failures on everything and everyone but themselves and take no responsibility for there poor choices or workmanship. Fortunately I also know some good ones that are craftsmen and want only the best for the people that they do work for and take full responsibility for their work.

Do what you want and sell that to others that can be talked in to it. I don't buy that is 100% safe and never will. so if you want to duct tape it and calculate the added support it gives the barrel wall, go for it.

You can have the last word because I am done trying to help you and don't plan on any more post on barrel wall thickness and will let the inter net experts decide their fate. I am sure that the membership is tired of this post and want to move on.

J E CUSTOM

 

[Edd]

I just looked at the thread specs for 1/2" x 28 threads. You would have about a .076" thick wall on a 30 caliber barrel.

If you then look at pressure rating for tubing, you will find that stainless tubing of a similar size will have a working pressure around 5000 psi. This is a continuous working pressure. The burst rating will be about 4 times that amount.

I'm not sure how much difference there will be between the different alloys of the tubing and the barrel. I would expect tubing to be a stronger material.

 

[FEENIX]

Jerry,

I am no expert, gunsmith, or metallurgist, but I just want to point out that I do not have any problem with you yielding caution towards safety; in fact, I commend you for it.

Cheers!

Ed

 

[rifle 57]

I am with J E Customs 100 % on this subject of 1/2 x28 threads on muzzle attachments with any bore larger than .264 cal. 9/16 or 5/8 on anything larger.

 

[shortgrass]

While in gunsmithing school, doing "open sight mounting" on rifle barrels, we were cautioned to not drill (for tapping) any deeper than to leave .150" between the bottom of the hole and groove diameter. Many front sights were soldered on because of this. Muzzle attachments weren't a big thing 25yrs ago, like they are now. But the same principals would apply to muzzle threading,,,,, no matter how 'perfect' you think your thread is.

 

[Pdvdh]

Better safe than sorry. My motto. I hate being the first to structural failure. Safety margins are standard operating practice where the cost of failures are high.

 

[J E Custom]

I just looked at the thread specs for 1/2" x 28 threads. You would have about a .076" thick wall on a 30 caliber barrel.

If you then look at pressure rating for tubing, you will find that stainless tubing of a similar size will have a working pressure around 5000 psi. This is a continuous working pressure. The burst rating will be about 4 times that amount.

I'm not sure how much difference there will be between the different alloys of the tubing and the barrel. I would expect tubing to be a stronger material.

Thanks Edd.

.076 is still 1/2 the recommended barrel wall (.150) to be safe. Quality barrels have to meet a very specific Mill analysis and test reports (MTR) and should be as good or better than low pressure tubing.

The exit pressure at the muzzle of most firearms is between 12,000 and 18,000 +/- and with back pressure applied by the brake It is higher. So you not only have burst pressure you also have mechanical pressure.

Another downside of this barrel thread diameter is the compression of the barrel tenon when the muzzle brake is tightened due to the thread thrust at 60o.

As discussed earlier, if minor thread diameters of smaller threads are used,9/16x28, the barrel wall thickness over a .308 bore would be .028 (5 times thinner than the recommended barrel wall of .150.

J E CUSTOM

 

[J E Custom]

Thanks Edd.



Another downside of this barrel thread diameter is the compression of the barrel tenon when the muzzle brake is tightened due to the thread thrust at 60o.

As discussed earlier, if minor thread diameters of smaller threads are used,9/16x28, the barrel wall thickness over a .308 bore would be .028 (5 times thinner than the recommended barrel wall of .150.

J E CUSTOM

TYPO, I meant to say Barrel tenon and Bore diameter.

J E CUSTOM

 

[jrock]

Another downside of this barrel thread diameter is the compression of the barrel tenon when the muzzle brake is tightened due to the thread thrust at 60o.

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?