CZ 550 Magnum is not a standard length action opened up. I have 4 of them. One is a 450 Rigby, one is a 416 Rigby. Other two are awaiting barrels.
CZ550 would be my choice.
I will take a photo later, I have some 510 Cartridges. I will place one on the follower to give you an idea.
If one was making up a 9.3x62, would one not use the regular Zastava action?
Anyone have an opinion on which is better the Demoulin or the Zastava. I would probably go over them pretty thoroughly so issues that one can machine out could be dealt with. Basic differences in materials, or set-up aren't going to get touched. I like the Demoulin safety for instance (as pictured).
Zastava:
Demoulin: