I have had an idea knocking around my head for a while, now.
Basically, a big bore cartridge. This would be a thumper, and probably cost ten dollars a round in a five-thousand-dollar custom rifle, but I just want to see if it can done. Eventually. When I have that kind of cash to blow.
Which definitely isn't right now, trust me.
So, I want to take the .505 Gibbs, a famous African hunting cartridge, and shorten the case to 2.950 inches.
I would open the neck up to be able to take .510 projectiles, which would enable folks to shoot surplus .50 BMG projectiles and an assortment of other projos in the .510 diameter category.
Overall length, digitally, at least, would be in the neighborhood of 4.580".
Yes, before you ask, it's meant to give the human race a chance in the looming robot/raptor/robo-raptor apocalypse. ;)
JBR Cola for scale. .505 Gibbs in the middle. .50 HRM is the big'un.