When it comes to copying miniatures - which is what making castings of an existing sculpt is, put simply - there is no "personal use" exemption. This question comes up a lot, and it always creates a long thread of people disagreeing about the "personal use" angle, but the simple truth is that copying/casting a miniature produced by somebody else is illegal unless the producer is also selling reproduction rights (which some companies do for things like horses, or body blanks, or weapons, and so on). As Bugsda points out, it then becomes an issue of whether - if it's for personal use - anybody is going to find out, but this doesn't change the illegality of it. All it does, in many cases, is make it an ethical choice, rather than a legal one. I'm sorry if it sounds like I'm on a high horse about this, but copyright issues affect me directly (in a different sphere), so I'm very particular about it.