Star Model A Vs Star Model B

so what is the Difence between the two other then the chambering?

i know the Largo runs around 30,000 PSI and puts a 128 gr bullet down range around 1100-1200 FPS

and the 9mm luger runs at 34,000 PSI and puts a 124 gr bullet down range at 1200 FPS..

are the recoil springs stronger or?