I’m surprised that the ‘safety factor’ on firearms seems to be so low. I realize that there are tradeoffs regarding weight, ease of maintenance, etc., but to hear that a double load of normal powder in a revolver cartridge could cause failure of the cylinder seems hard to believe. I know industrial lifting equipment has a safety factor of five or more. Granted, such equipment isn’t supposed to handle such extreme loads over and over and over again, but still…
True, black powder is not used in ‘modern’ firearms, by definition if ‘modern’ is defined, as it sometimes is, as guns designed to use smokeless powder*. But to semi-nitpick a little further real black powder isn’t commonly used anymore even by most ‘black powder’ arms owners. Most people use substitutes, a semi-generic term is the brand name Pyrodex. It acts like black powder in terms of internal ballistics for a comparable volume, but has the ignition and storage safety characteristic of modern propellant. Real black powder might be used by purists, especially since the modern stuff can have trouble as the priming powder in flintlocks, but the great majority of ‘black powder’ arms are percussion cap primed. Real black powder isn’t carried by some gun/ammo stores anymore.
*although the US federal definition only includes cartridge guns made after 1898, so quintessential modern military rifles like Mauser bolt action smokeless powder repeaters are antiques and not guns under US federal law if the receiver is stamped with a manufacture date prior to 1899. The mass of weapons made to the same designs since 1899 are modern, legally.
Different industries use different safety factors. E.g. airplanes are designed to catastrophically fail at 1.5x the rated maximum loads. Which rated maximum loads are themselves ~2x more than are seen in a typical day. But which may well be seen on any given particularly bad day. This in machines meant to endure tens of thousands of workdays.
In the case of firearms, one of the issues is that the powder burning as designed and producing the expected time vs. pressure/temp/volume curve of combustion gases depends on the packing density.
An inadvertent overcharge also causes a higher packing density. Which causes more rapid burning. So e.g. 1.5x the powder might have 5x the peak pressure and achieve that peak in half the normal rise time. Which is to say you’ve got an exponential situation which looks from the outside like a brittle failure mode: everything’s fine until suddenly it’s catastrophic with no “yellow caution zone” between green and red.
Another issue with hobbyist loaders is as Loach said above. There is an established ethos of squeezing the absolute max out of any given cartridge / powder / bullet combo. Men and toys are like that.
Hobbyists carefully make ever more powerful loads until they detect signs of incipient or partial failure. Then they back off a smidgen. Probably not considering their own batch to batch production tolerances when deciding how much to back off.
By design the cartridges are the first to fail, not the firearm. But somebody who makes a habit of running his cartridges at the brink of failure every day is riding his firearm pretty hard as well.
Thanks; I did not know that.
What would be the evidence of cartridge failure or incipient failure, such that one would back off on one’s loading?
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Although there is a certain thermodynamic advantage to detonation of an energetic material versus combustion of the same material, but because the pressure wave is so intense the stresses will require a much, much heavier pressure vessel. This would also definitely cause issues with recoil and gas operated weapons since they depend on experiencing a specific range of pressure profiles to function correctly, and detonation often has greater variability in pressure profiles compared to combustion phenomena.
Stranger
It’s been awhile since I did metallic cartridge reloading, but this article at accurateshooter.com goes into some of the signs to look for in your fired brass cases. They mention things such as: ejector groove marks on the head of the fired case, sticky or difficult bolt operation, difficult extraction of the case from the chamber.
They find less reliable, signs that I used to look for as evidence of too high chamber pressure: flattened/cupped primers, cracked cases or bright rings on the case. Other sites and reloading books mention greater recoil than normal as evidence that perhaps pressures are getting too high.
YMMV, but I never saw the point of pushing things to max and beyond in my very limited experience reloading. I found minimal any velocity gains and consequent improvements to drop and wind drift. Moreover, in my rifles, the higher velocity loads were less accurate off the bench, though admittedly, not grossly so. I reloaded to be able to obtain very accurate cartridges, with the terminal performance I wanted on game, at a fraction of the cost of comparable factory ammunition. Not to wring the absolute last 100 FPS out of my rifle. Again, YMMV.
Examining the used cases would tell if the loads were too hot. Cracks, tears, splits or other deformities would be a sign that that there was too much propellant in use. Here is a site with pictures of reload failures.
ASME standards for below the hook lifting devices (anything that a crane uses to attach to a load) has a typical required factor of safety to yield of 2.4 (may be higher if the device has low strain capability or is carrying hazardous loads.
Firearms are designed to meet the SAAMI spec pressures or “typical” load pressures of unspec’d cartridges to a burst factor of somewhere around three. What is more critical is that the firearm can experience complete blockage (obstruction in the barrel) and the barrel may bulge but not burst. Making the barrel, and in reciprocating actions, the slide or gas piston, capable of resisting substantially greater pressures would require making a much thicker barrel and heavier slide, which would both increase the size and mass of the weapon, and for recoil operated weapons, interfere with operation at normal operating pressure, so there is a balance between reasonable safety versus reliability and functionality of the weapon.
Stranger