With all due respect to my friend Doug, It would probably be better if you realized there is some chance of damaging a pattern stock regardless of tape covering. All stocks must be jigged fore and aft to accommodate mounting in the machine. With a shotgun stock the "head" of the stock must be bridged with the mounting device which is normally epoxied to the front (and maybe rear) of the stock. Attaching or removing this may cause damage.
None of the stock duplicators that I have worked with will guarantee no damage when machining from an existing stock.
Best,
Steve
