Originally Posted by 308 nate
Okay so here's what I am understanding.the minimum muzzle diameters is referring to Minor thread diameter.I will list UNR minor diameter Max Ref A3.
1/2x28tpi= .4574 so .140×2=280+bullet diameter.224= .504
9/16x24tpi =.5129 so this would work for.224.and .243 of your willing to cross the line.
5/8x24tpi =.5754 so .140×2=280+bullet diameter .308=.588 so .338 would be out of the question.My question then is this a line not to be crossed.I have talked to many barrel manufacturers as well and they recommend .15 minimum wall thickness on stainless, which I do follow for fluting .I would be interested to hear what your minimum thread diameter and pitch per caliber would be for stainless steel and chrome moly,and if you treat them differently?please forgive all of my questioning. I am just trying to understand what you're saying. I have literally put hundred of breaks on 30 caliber barrels with 1/2x28tpi with zero problems. in fact in the early days I even threaded a few .338 barrels 1/2×28tpi with no problem, although this does not meet my current guidelines. All the best .308Nate
Thanks Nate, your Questions are good.
The Engineers are using .140 as a safe wall thickness based on what I have been told.
I actually use a minimum wall thickness of .150 on all of the calculations regardless of barrel material. .010 thousandths is not very much more but it is more.
Different thread pitches have different thread major and minor diameters and I try to select the largest thread diameter above the minimum wall that will exceed the minimum requirements.
In other words, if I can use a 5/8x24 thread on a .224 barrel as long as I have enough shoulder to seat/time the brake even though I could use a 1/2x28 I do.
I have seen muzzle brakes that were shot off the barrel (For many reasons) that took the tenon with them. In every case it was ether the tenon thread was to small, the brake was to thin, or the threads were poorly done and in some cases the bullet was striking the brake and took the brake with it.
I see lots of big bore rifles that have no provisions for a muzzle brake because the barrel is to light
to thread so I don't.
I consider myself fearless and the thought of placing a brake on a .338 using a 1/2x28 thread pitch scares the hell out of me. I am glad that you have not had a problem with the 30s and the 338s with such a thin barrel wall (The .308s would have a .074 thousandths wall thickness and the .338 would have a.059 wall thickness) making the .308 1/2 the recommended wall thickness and the
.338 1/3rd of the recommended minimum wall thickness. and if that doesn't scare you I would not want to piss you off.
This is truly a case of more is better but IMO less is unsafe and should never be used.
And yes I do draw the line at .150+ wall thickness and if the barrel is above this minimum I will use the largest threads possible to increase the wall thickness.
The numbers on the chart are a little conservative (+ .010 )but not so much as to make it difficult to do the job. It is intended to be a guide line to answer the question for someone that doesn't have a machinist or gun smith background that may be thinking about installing a brake on a light contour barreled rifle.
Thanks again for your questions and I hope I answered them to your satisfaction
J E CUSTOM