There are several methods of making prototypes.
The method depends on the factors you wish to test.
The only way to truely emulate all parameters is to make a prototype mould and produce mouldings in the exact same material.
To test type shape and fit, SLA is very good.
To get some idea of strength, machined parts from bar stock can work, but, extrusion grades of material tend to be tougher and maybe not quite so rigid and the machining process removes skin layers and leaves notches, both of which can have a significant effect on strength.
Sometimes a very simple mould in epoxy can be cast off a SLA or wood or whatever prototype. This can be inserted in a bolster and a few mouldings taken off. Once again, limitations on pack pressure and effective cooling rate can change physical properties a bit.
Regards
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