Firearm damage from high pressure rounds

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Alpheus

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Having a Facebook discussion about reloading manuals and pressure and it got me thinking. We've all seen/experienced what happens when you super-charge a reload and the gun blows up. What happens if you feed your firearm a steady diet of above max pressure reloads? Not enough to go ka-boom, but significantly over SAMMI max. Over time, does it result in mechanical or metallurgical damage to the firearm, and if so, what kind?
 
If the hoop stress on the barrel or bolt thrust strain on the bolt lugs is above the elastic yield strength of the steel, it will deform. If it isn't, it won't. Highly dependent on lug size, barrel diameter at the threads, steel alloy, and heat treatment.
 
The metal will stress, and over time micro cracks will form inside until one time it wont hold and will blow apart.
I could understand making an overcharged load by accident, but feeding it a a steady diet of above max loads ? Why would you even think of doing something like that unless you have a death wish.
 
I think the first damage you would see is from failed primers causing gas cuts in the bolt face and firing pin tip...
 
I know a fellow that had an old 98 mauser in 30-06..

His previous 30-06 was a new savage. He fed the old Mauser a steady diet of the super HOT loads he ran through his new savage.

After 2 or 3 rounds the bolt would become stiff and extraction problems would arise. His primers were as flat as flat could be.

After a couple years of that he eventually set the bolt lugs back and the rifle started having light primer strikes and all kinds of weird issues.
 
Some adventurous individual decided to load his 223 Ruger No.1 a bit on the warm side. Known to be a strong action. Apparently he was getting 4000 fps muzzle speeds and his particular rifle was none the worse for having done that. However the brass didn't fare as well. Not recommended of course. :eek:

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Magellann said:
The metal will stress, and over time micro cracks will form inside until one time it wont hold and will blow apart.
I could understand making an overcharged load by accident, but feeding it a a steady diet of above max loads ? Why would you even think of doing something like that unless you have a death wish.
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"Maximum" is a variable that is different for every rifle, rather than being based upon any realistic set point. Action sizes and materials vary, the quality of the fit of the parts varies, and the particulars of reality vs. specifications of the steel used, and it's inherent flaws, varies.

Reading and following the reloading manual is a safe way to go, but it is very possible that the "maximum" loads listed there are neutered down to be used in some really questionable pieces of hardware too. Load manuals are filtered through liability lawyers.

End of day, each rifle is it's own individual case, and must be adjudged accordingly.

Depending upon what exact form of "maximum" loads are used, the net result might be nothing at all, might be a gradual and predictable destruction of a firearm, or it might work just fine until one day it decides to disassemble itself at speed.

From the theoretical aspect, it comes down to engineering student homework, using Hoop stress, and other stress analysis on the various parts, using values decided upon as representative of what the materials are supposed to have. Lots of higher maths and (preferably) computer programming.

Lots of blown up gun pictures around. Not that hard to form an opinion of how they are most like to come apart even for a layman. But I would not be betting my grocery money on any one failure mode to be likely. If at all. Too many uncontrolled variable to deal with.

Cheers
Trev
 
That all makes good sense Trevj, I wonder if the firearm manufacturer would tell you what the max safe load would be for their rifles.
 
Starting point for a stress analysis is to review the MTR's (material test reports) for the steel used to fabricate the various rifle components. AISI 4140 is typically used. Its yield strength can vary depending on hardness.

Then a means to accurately measure chamber pressure for a given load such as a strain gauge set up.
 
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Magellann said:
That all makes good sense Trevj, I wonder if the firearm manufacturer would tell you what the max safe load would be for their rifles.
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They do. It is the given max pressure associated with the SAAMI specs for the cartridge type stamped on the barrel. There is absolutely no commercial value in blowing up a few of their rifles just to be able to give a higher than SAAMI chamber rating. 99% of gun owners wouldn't know what to do with that information, and 99% of handloaders don't need it, as they know how to detect pressure signs by the brass and do not measure chamber pressure directly. So what, Thousands and thousands of dollars spent in RnD so one gun owner in 100,000 can know what the chamber pressure was when he blew up his gun?
 
Slamfire said:
Would be nice to know what pressure levels my handloads are at. :cool:
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Isn't there a program that'll give you pressure estimates based on how much powder, ect? QuickLoad maybe? (I dunno, I haven't gotten that deep down the rabbit hole yet, but I see it mentioned from time to time)
 
Yep, QL gives you an idea - based on a whole bunch of assumptions. I'm pretty sure that with some of my particular rifles the maximum loads listed in the manuals are quite conservative. Only way to be sure is to accurately measure chamber pressure for whatever load.
 
Slamfire said:
Yep, QL gives you an idea - based on a whole bunch of assumptions. I'm pretty sure that with some of my particular rifles the maximum loads listed in the manuals are quite conservative. Only way to be sure is to accurately measure chamber pressure for whatever load.
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But do we even really need to know the objective number? For most handloaders all wee need to know is safe/not safe. I can't imagine a scenario where knowing the number would actually help in any way.
 
I definitely would like to obtain a strain gauge some day. A .473" diameter cartridge should easily be able to exceed SAAMI pressures with no problem in an action that was designed for 65ksi .532" diameter cartridges. Even more so for a little 223 Rem in a full size action like the Ruger #1 (as mentioned above) or even a Rem 700 or Savage 110.

I run QL-estimated 60ksi loads in my Mauser 98; higher than CIP but sure to be safe. Also, some rifles have barrels that just run faster with lower pressure than others. And vice versa. With hard primers and good brass you could be dangerously higher than SAAMI without knowing it. Or you could be leaving lots of performance on the table. Only a strain gauge will tell you the actual chamber pressure. Then math tells you if the action/barrel can take it. Even then there are unknowns as to the exact alloy and heat treat. You can measure surface hardness but that isn't 100% reliable.
 
Just to know is reason enough for me. An accurate, economic and easy to use strain gauge set up to measure chamber pressures would be totally cool. Then you would know for sure the pressure wave characteristics of your handloads. The software and the usual signs to watch for are rough approximations at best. Experimentally stress testing your handloads with instrumentation would be a lot of fun.
 
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