Okay, so at this point (using your ''0.32-inch x 21 millimeter'' design pushing a 90-grain projectile at 1,150 fps), you've basically reproduced the .30 Luger, which slightly out-performs your proposed cartridge with a .308''-diameter, 93-grain projectile @ a nominal 1,220 fps. Predicted BRL incapacitation is 60.44%.
Varminterror is very much 'spot on' with his assessment that the proposed round doesn't have anything more to offer than the .380 already does; the BRL incapacitation equations (as coded against 7,898 wound data in the WDMET database) bear that out in my prior responses and analyses. Folks seem to want what you are pursuing (that is, they want greater terminal performance than the .380 in an ''easier-to-handle'' package), but I am almost certain that the course that you are pursuing has already been attempted (approximating the .30 Luger) is not going to achieve that result as it has already been tried and abandoned for less than successful results. I am sure that you've devoted considerable time researching the matter, but I also believe that you are still very far from "
bridging the gap between 'tiny & weak' and 'too big and too little capacity' " with the course that you have chosen.
If we were to assume that you would load your design with a 0.3125''-diameter, 90-grain JHP @ 1,150 fps that expands to 1.5x its initial diameter (thinking Hornady XTP here
), its probability of incapacitation increases to 66.7%; barely surpassing that of the 9mm 115-grain FMJ (65.97%) evaluated in an earlier post. Penetration decreases to a much more desirable predicted range of 13.36 inches (MacPherson model) ― 14.55 inches (Schwartz model), but the modeling still suggests that the 9mm 115-grain FMJ beats the best that the ''0.32-inch x 21 millimeter'' design can optimistically promise. I think that the best answer that we've seen to date is the Sig P365 and it uses a cartridge that already exists, can be purchased very inexpensively that has established quite a long track record with both expanding and non-expanding projectiles that will probably not be surpassed by the proposed design.