Jason, your design parameters seem to be fluctuating?
Sorry, I just can’t seem to nail down the idea of what you’re looking for, at least not enough to be of any help. I thought it was .30 or above bullet dia. in a small diameter case and of intermediate power. Oh well, I guess I'm still confused?
ME, while extremely important, isn’t the be all and end all of performance. Bullet diameter, shape, and weight also play a huge part in determining how well a particular job is done by the bullet. Design concept is always done in reverse; whether you are attempting to copy an existing piece of technology, or figuring out how to achieve a specific goal. Decide upon a goal(what the bullet needs to do). Reverse time in your mind, using your goal as the anchoring point, rather than trying to build something from scratch using the beginning of the prototype as your anchor. The thought process of creation, involves reversing the thermodynamic arrow of time, imo... from end all the way to the beginning. Creation is the beginning and end. All else is engineering in reverse (done in your mind), and engineering foreward (done by hand).
Without the military adopting the 6.8 SPC, it was doomed to failure in the civilian market. Aside from a very narrow niche. (and other, already established, civilian rounds are in production that fill the niche quite nicely), anything it can do, either the .308 or .223 can do better. I suspect that the military came to pretty much the same conclusion due to practical concerns.
Keep smiling ... it'll just make 'em wonder what you're up to...