Again, however, I ask the question of how BP only proofs affect value of gun? With peoples inclination to use vintage guns on SC's, etc my better judgement suggests a deduction in value. Further, were I ever to sell gun, I would feel compelled to disclose the BP proofing. On the other hand it is a nice old gun I'd really like to own & hunt. I just don't want to invest a significant sum in something I have heard might warrant a 50% discount.
Erik, It strikes me the answer to your question about values is quite easy.
If it is only BP proofed and you are concerned about reselling down the road at a discount, aren't you buying now for a discount? Thus the relationship between your "buy now" price and your "selling down the road" price the same.
Or is the asking price for the gun now set as though it was nitro proofed?