Why are there so many different calibers, and so many in oddball sizes, for rifle, and to a lesser degree handguns?
Military cartridges reflect the doctrines of their time. The first smokeless military cartridges, they really, really thought that their troops would be shooting at advancing men at extreme ranges.
Just take a look at the rear sight of a M1903. The powers that be expected American troops to volley fire at 2500 yards! The battle sight was zero’s at 500 yards!
It did not help that when the British engaged the Boers, many of the Boers were expert shots at long range, and caused a lot of casualties with their 7mm Mausers, and the average Tommy could not hit the berm from which the Boer was hiding. A word of advice from the times was “
stay away from Officer’s and white rocks!”
While the Swiss K31 rear could be zero’d at 200 yards, they were still thinking of shooting at things at 1500 yards. The previous rifle, the K11, the rear sight lowest setting was 400 yards. So the Americans were not the only ones thinking of extreme long range rifle fire.
Military cartridges were developed around a number of criteria. Think zero space, recoil, lethality at distance, combat load, etc. I don’t think barrel life was a consideration. Depending on the weighting of these criteria, you end up with military cartridges between the 6.5 Carcano and the 8 mm Mauser, with the 8mm Mauser being an early smokeless military cartridge, and particularly well designed for its era. The largest honker I am aware of, as a service rifle cartridge, is the 8 X 63 Swedish, and the recoil with that must have been brutal. But, the thought process behind a military cartridge was a detailed process, usually involved a lot of testing and trading of parameters.
Notice, no 416 Rigby’s or 460 Tranasaurus Rex cartridges as military cartridges.
Post WW2, everyone threw in the towel eventually and gave up believing their troops could hit anything at or beyond 300 yards. Sure, the pre war troops marksmanship was good, but they were all chopped meat before 9 months was out, and replacements called themselves “cannon fodder”. Sammy, our last living WW2 Veteran had 20 rounds of familiarization before being second wave at Iwo Jima. Sammy always believed if his Dad had not taught him how to shoot, he would have never have come back alive. My Uncle, 101 Airbourne, dropped into Normandy with just 8 rounds of familiarization with his 1919 machine gun. He could salute and march in formation with the best, but there just was not enough time to turn these guys into good shots. At the peak of the war, the US was experiencing 60,000 causalities at month, 20,000 of these dead, and the other in various states of disassembly. Believe it or not, we did not have enough bodies to conquer Japan, based on the losses we experienced at Iwo Jima. A big reason they used the bomb.
So post WW2, what you find are new military cartridges of lesser power and range than pre WW2 cartridges. Which were all hold overs from WW1.
Commercial cartridges are not the result of careful analysis of parameters, nor do they show any logic other than maximizing the profits of the corporation introducing them. Each cartridge was rolled out with noises greater than that of the Archangel's trumpet at the second coming of Christ. And of course, each cartridge was sold as filling an essential need. The gap of which between existing cartridges greater than the Grand Canyon. If you go through the book Cartridges of the World, which is the size of an old city phone book, you observe differences between cartridges are infinitesimally small within their respective “groups”. Of course there are the rounds guaranteed to knock a dinosaur on his butt. Lots of dinos roaming those woods!
There have been so many cartridge introductions that for rifles, as an example, the gunwriter’s have a clear set of selling points and procedures which we all have read again and again. The current craze is accuracy at extreme range, so similar what Jack O'Connor wrote in his day: kinetic energy is equated as lethality, bullet drop at range is emphasized, but instead of distances between 400 and 600 yards, the wonder cartridges are touted for shooting critters at 1500 yards! Unlike the bullets of yore, ballistic coefficients are perhaps the greatest selling point. Drift at 600 yards was used as an example of the superiority of modern bullets. The comparison was one inch of bullet drift less at 600 yards than the old bullet. This works when the buyer is clueless about the magnitude of wind movement that happens at distance, the absolute inability to measure wind speed and direction, even on "good days", and that the wind is totally unpredictable. Wind speed and direction are neither uniform nor linear. I have looked at the 600 yard target, the flags, the mirage, rolled over, fired a shot, only to find between scoping, a fishtail pickup happened and the bullet moved out in the eight ring, about three feet! There is a reason target shooters get sighting sights, something hunters don't get.
Today’s cartridges are being sold based on tiny differences as throat freebore. A whole crop of them has recently been introduced in the 277 caliber. Some so dimensionally close to one another, you can’t tell which is which in the picture!
If the manufacturer can get you to buy the latest and greatest cartridge, then a train load of money is following. New dies, new bullets, new brass, new trimmers, new powder funnels, new case holders, just think of all the junk you buy with a new caliber. It adds up to a lot of profit.
Product development cycles shorten every year. Manufacturers are frantically throwing cartridges against the wall, like jello, hoping that some of the fusillade will stick. And then, next year, today's greatest and latest cartridge will be old hat. Take as an example, the 270 WSM and the 6.8 Western. Hardly any difference between the two, the differences primarily created to give the appearance that the 6.8 is a new cartridge. Oh the 270 WSM was good in its time, but now, so obsolete. And, you have to have a new rifle to go with it.