New Cartridge Developments and Implications for Dismounted Infantry Soldiers

[stanc]

The problem with the SPC case length is that there is not enough room for a decent ogive within the AR15 magazine length.

Shortening the case moves the optimal caliber in the direction of 6mm or .25 so the velocity can be kept at OK levels.

Don't shorten the case. Lengthen the receiver. Historically, whenever a new cartridge has been adopted, new weapons have been developed specifically for it. Which means the AR15/M16/M4 magazine length is probably irrelevant for military use.

Then load a long-ogive bullet in the case. Like below (except with lead-free construction, which would make the bullet substantially lighter than 135 grains).