Why would anyone venture outside published data limits? I ask that question for a reason:
1. There is a reason
2. How do we know it’s safe?
I’ve put my load data out there, including the ones that are outside published max (with disclaimers)
However
Why is +P generally OK with pistol?
How much +P is too much plus?
These are all good questions. I have met gentlemen who worked on the determining boards of Industry Standards Groups. And I have talked to those who determined other standards. Standard development is often very raucous just like the debates we read in the threads on these forums.
Lets assume that pressure limits were determined rationally. The first step for pressure standards, the way I would do it, would be based on structures and loads. Not merely what would the structure take to immediate failure, but the load it would take for eventual structural failure.
This gets us into the issue of service life. This is very important, all mechanical items are designed to a service life/duty cycle. Fatigue is real, and even with a safety factor of two, or maybe three, or maybe eight, materials degrade with use. Steels that could have supported a 200 % load when new, after much use, maybe they are down to 150%, or 125%. When they have a lot more use, sometimes the part is so weak, that it cannot support the original 100% load, and that is when the part breaks. Steels develop micro cracks with use, the part becomes weaker.
I have seen a denial of this in the shooting community, particularly in regards to old service rifles. Owners want to believe that the things will last forever, because they have been around forever, and when you are dealing with WW1 era steels and WW1 era firearms, just how many rounds the receiver has seen, and just how many rounds the receiver can take, is a big unknown.
https://thefiringline.com/forums/showthread.php?t=422346&page=3
1915 swede 6.5x55
sorry for the highjack
but i have or had lol sporterized m96 carl gustav 23.5 barrel shot about 100 rounds from it no issues reloaded to speer military spec starting load and coal 140 accubond then kaboom after one weekend the reciever exploded and im lucky to be here
i checked firing protrusion and its within spec 39 grains rl 22 win larg r primer once fired nosler brass no probs before prob a flaw in reciever from being so old?
any help appreciated now to commercial actions
Note: Barnes bullet, minimum load with a 140 is 40.4 grains RL 22, max is 44.9
Duty cycle is an interesting number that no one publishes. Duty cycle can be defined a hundred different ways, but let’s say that duty cycle is the maximum number of maximum pressure loads that a rifle locking mechanism can take before the lugs crack. We know the US Army requirement for a service rifle was 6,000 rounds. The Army wanted a rifle that could fire 6000 rounds and not break. A bud of mine worked on the Anniston Army Depot line, and a random rifle was pulled from a lot of rebuilt M16's, and is fired 6,000 rounds as a quality check. For any rifle to complete 6000 rounds without failing it obviously must be able to fire more. And what you find on AR15.com is that AR15 bolts typically fail around 10,000 rounds, some fail sooner, some fail earlier.
High round count AR/M4's (over 100,000 rounds) and how they have handled on our range
https://www.ar15.com/forums/ar-15/H...ow_they_have_handled_on_our_range/118-677135/
What % of bolts fail MPC testing?
https://www.ar15.com/forums/ar-15/-/12-290916/
But if Stoner designed his bolt to survive 6000 rounds without failing, and applied a safety factor of two, then you would expect to see the average bolt break around 10,000 rounds or more. What is surprising is to see reports of bolts failing at 3000 rounds. Improved material technologies have extended the life of the AR15 bolts, Army Marksmanship Unit shooters told me of bolts they were using that were lasting 30,000 to 40,000 rounds.
But no man portable rifle or mechanical mechanism is designed for an infinite number of duty cycles. No mechanical or civil structure is built for an infinite lifetime, except perhaps, the Pyramids. Build any locking mechanism to the weight of even the smallest Pyramid, it will last an infinity of standard pressure rounds, but the rifling will still wash out. Build a rifle not to weigh more than 8lbs, stock, lock, and barrel, and the designer has to accept, even if the user does not, that the locking mechanism will fail after a certain number of rounds are fired. You can expect that the lifetime of any light duty firearm to be in the tens of thousands of rounds, like 10,000 rounds, 20,000 rounds, don't count on it lasting much more with maximum pressure loads. Might in fact, last less.
The M134 minigun is an example of a military firearm whose service life was increased with product improvement programs. Obviously more modern materials were used, and modern structural analysis programs were able to analyze to a much finer detail, load paths, and material stresses. The mini gun is much heavier than any sidearm, and you have to take into account the weight of the 125 pound ammunition feeder, and the electric generator.
The Evolution of the M134D Minigun
https://www.defensemedianetwork.com/stories/the-evolution-of-the-m134d-minigun/2/
Early weight-saving investigations included the development of a titanium housing and a titanium rotor, which lowered the weapon weight for a new M134D-T (titanium) design from 62 pounds to 41 pounds.
“The titanium housing was great,” he added, “except that after about 500,000 rounds fired – which, in machine gun language is a very large number – a portion of it would start to wear out. Again, 500,000 rounds is a massive lifespan. Most machine guns have a life of about 40,000 rounds before you change them out. But we decided that we could save a whole lot of money and only gain 1 pound back by changing the housing back to steel. And you went from the decremented life of 500,000 rounds back up to the normal life of 1.5 million round
https://www.garwoodindustries.com/qualify.html
Documented Old standards, (2006): 25,000 to 30,000 rounds between failures (RBF).
Documented G. I. standards, (2011): 150,000 to 500,000+ rounds between failures (RBF).(Army test
report available).
So, lets say we have pressure standards that were established during the WW1 period. I written extensively on the poor metallurgy of the era. The 38 Special loads of the time were entirely appropriate for the plain carbon steel, non heat treated revolvers of the era. Firing the loads of the day, in the revolvers of the day, you should expect to any period revolver to last its "expected" service life. By the time you get to WW2, the very same revolvers, or later versions, are being built out of alloy steels, whose yield strength is at least 20% higher than the plain carbon steels used in an earlier version. The fatigue lifetime of the same part is also increased, at the same load, by the use of alloy steels, over plain carbon steels. If you knew the material was better, if you knew how it was heat treated, then you could reasonably say, upping the pressure of the cartridge a bit, would give enhanced cartridge performance, for the same revolver lifetime. Therefore a +P load would be fine, as long as you don't stick them in an older revolver, which would be damaged in a short amount of time, because the structure was not able to handle the higher pressures loads.
I know pistols shooters who have shot 600,000 rounds, and 250,000 rounds through their K frame S&W pistols in PPC or Bullseye competition. Both of these gentlemen were shooting 148 LSWC's and 2.7 grains Bullseye. This is a very light load. What wore out were extractor stars, cylinder hands, but the cylinders, barrels, and frames were still good. However, one of the shooters competed in events that required "major" loads, and he had cracked the end of a K frame barrel. You shoot low pressure loads, things last longer. You shoot high pressure loads, things wear out sooner.
The 257 Roberts is a cartridge dating back to the WW1 era. The rifles of the era were made out of those plain carbon steel, crappy metallurgy, steels of the day. A large number of those rifles were built on WW1 era Mausers, which were built for a 43,000 psia 7mm or 8mm Mauser service cartridge. Pressures for the 257 Roberts has been kept low, because of the liability to the cartridge manufacturers. I don't know when industry offered a +P 257 Roberts, but that was not too long ago. You know, if you have a modern rifle, made of modern materials, made for the 257 Roberts, there is no reason to keep your cartridges to less than, or equal to, 43,000 psia. So, why not a +P rifle cartridge for a very old round?
