When 450 Marlin was introduced 45-70 factory loads were all black powder level loads. In other words very weak. The only way to get modern more powerful loads was to handload. At the time most factories were afraid to load modern loads out of fear they would get into an old 1800's rifle and blow it up. The 450 Marlin gives modern 45-70 loads, but in a case that can't be chambered in older rifles. Today there isn't much need for 450 Marlin since we can now buy hotter 45-70 factory loads.
The 444 was introduced in the 1960's and was basically a flop because all of the bullets fired out of it were designed to work at handgun velocities. Marlin revived the 45-70 from the dead with the plan to discontinue 444. But better bullets designed for it finally were introduced and it has caught a 2nd chance.
The 300 WSM is really misunderstood and one of the better new options in my lifetime. Compared to 300 WM it uses a more efficient case to come within 50 fps of 300 WM speeds, but it burns 10-15 gr less powder resulting in significantly less recoil. And much better accuracy. Due to the reduced recoil, and short action cartridges,it can be built in a smaller, lighter, more compact rifle. Which is exactly what the inventor was trying to do. Unfortunately most manufacturers don't seem to understand this concept. In the right rifle the 300 WSM is a great cartridge and I'd take it over any other 300 magnum 10 to 1.
The man, Rick Jamison, who invented the 300 Jamisontried to sell his idea to Winchester, who declined to buy. But shortly after introduced the identical 300 WSM. Jamison sued and won. Jamison now gets a royalty for every 300 WSM sold. Ruger didn't want to pay the royalty and introduced the similar 300 RCM, Remington did the same thing with the 300 SAUM.
The 375 and 300 H&H cartridges are extremely long and either require a magnum length action (which almost no one makes anymore), or you have to take a long action and modify it which is less than ideal. Either way results in an extremely expensive rifle. 375 Ruger easily fits in a standard long action and can be sold much cheaper. And it gives a bit more power.
6.5 Creedmore...... Already got the 260 Rem...... And the 6.5 Swede
The 6.5X55 was designed to shoot 160 RN military bullets. The 6.5X55 has been around since the 1890's and factory loads are kept anemic. Plus rifle specs are all over the place. The only way to get a 6.5X55 to shoot is to go with a custom build and handload cartridges to modern specs.
The 260 was designed around 120 gr deer hunting bullets. Long range target shooters discovered that by loading cartridges with 140-150 gr hi BC bullets they could go great things at long range. The problem is that these loads wouldn't function in factory 260 rifles. The 6.5 CM was designed to offer out of the box rifles and ammo that would duplicate what they were doing with custom rigs and out of spec hand loads.
Y'all ever notice, while new cartridges generate sales, any time they introduce a new model rifle, their first chambering is usually .30-06?
Not anymore. Several new rifles have been introduced in recent years that aren't even offered in 30-06. I saw some numbers for new rifles produced in 2018. The 6.5 CM accounted for almost 1/2. The 308 was at 5%. The 30-06 was lumped together in the "other" category.
