I have a '61 thats still shooting.
I use 22.0 grains of 4227 under a 240 grain soft point. Its fast, real fast
Top end bullet weight really isn't an issue with this gun assuming you don't make the oal length to long to go through the action and or fit your chamber. I've yet to find a factory load it won't handle.
What I have found is the faster burning powders will not make the gun cycle. Back when I still had a .44 mag handgun (someday I'll pick up another), I loaded up a lot of rounds using Red Dot. Works fine speed wise but burns so fast the pressure drops off to quickly and inturn won't cycle the Auto Carbine.