I would use the Max case for all the loads, just reduce the powder charge (assuming your going to reload).

I have a Low Wall that's a 357 Max with a 28" re bored, original barrel. I've shot 150gr GC SWC at almost 2400fps, 208 GC at almost 2200 fps and 210 PB at 1400 fps. I'm sure you could work a Unique load up that got you down to 1200fps with a 150-160gr pistol bullet. You would be able to easily tell the difference between them by the bullet shape. Your sight setting would be the biggest problem. I think the bullet jump would destroy the accuracy with the specials and mags.

Let me know when you get it ready to shoot and i'll give you my load info.

Frank

On a Martini cadet you will need to do something with the breach block, them long cases don't bend enough for loading and unloading. There is usually enough meat in the top of the block to cut it down some. Another help is to weld the cocking lever and recut the sear notch so it will hold the block all the way down.