I understand you are looking for a name for a ctg. that has no case or ballistics.
.500 GK (Giant Killer)! would that work?
I'm sure tinker was simply concerned about the ballistics end of your description of your "new" round & offering suggestions of rounds that would work.

There were two aspects of your thread, second listed in your 2nd post.

You noted:"Im NOT thinking of this as a hunting cartridge, rather a point blank stopping cartridge where even a 44mag would do."

tinker was merely putting forth his thoughts on this.

Your last post is out of line, in my opinion.

Of course, to be a Howdah, it has to be a side by side, or side by side over/under with 4 bls.
Likely a rimed case would be easiest.

Who's going to build it? Perhaps getting the gun together first, then naming the round you've chambered (if it is not a copy of another round), would be the way to go.