Considerations on the Evolution of War

[stanc]

All three weapons must -

Use a common magazine that holds a minimum of 25rds, weighs no more than 1lb, and is within +/-3% of the size of current STANAG magazines.

Use a common magazine that holds a minimum of 25rds - Since the standard magazine capacity for the last few decades has been 30 rounds, I can't see the military going to less. I'd suggest 30-rd minimum.

Weighs no more than 1lb - That should be no problem. IIRC, the steel 30-rd FAL mag weighs about 0.75 lb. A polymer 30-rd 7.62 NATO mag would weigh about half that.

Within +/-3% of the size of current STANAG magazines - Not possible with 30-rd mags for any cartridge with case diameter significantly larger than that of 5.56 NATO. For example, 30-rd 6.8 mags are about an inch taller than 30-rd 5.56 mags. (Also not possible with mags for any cartridge with OAL significantly longer than that of 5.56 NATO.)