A wildcat rifle made with 50 caliber shell caseing necked down to 8mm?

The Army went to a gunmaker, many years ago (about 50) to see how much velocity they could get out of a rifle. Purely as an experiment. He got an 87 grain .22 caliber bullet to gravel at a little over 6000 fps. The bullet disintegrated on the target. That was the end of that story. Many tests have been done trying to push bullets as fast as they can go and still get accuracy. There comes a point with every caliber where the increase in velocity of a given projectile requires a disproportionate amount of powder. The optimization of powder for bullet weight for caliber is generally termed "bore capacity". The current available cartridges in 8mm are already "over bore capacity" and the amount of powder you could pack into a necked down .50 cal. machine gun cartridge would certainly be way over bore capacity for that caliber. Then there is the factor of recoil. I actually owned and shot (only 9 times, all I could handle) a .378 Weatherby Magnum. This was the .460 Weatherby Magnum case necked down to .375 caliber. I couldn't handle the recoil (I'm 6'2", 200 lbs). My favorite two guns are the .300 Weatherby Magnum and the .375 H & H Mag. I mention this to show that I don't mind heavy recoil...but there was a limit. So, if you want to try this as an experiment and just for the hell of it, go for it. I suspect the recoil would be horrific, the amount of powder would be enormous, the flame of unburned powder (and burning powder) coming out the muzzle would be awesome, noise also big. And I don't know what in the world you could do with it (other than write a magazine article). But go ahead and have fun if it is something that pleases you.