empirevr

Regarding your question about
One often sees old hammer rifles marked as being 'nitro proof'....now what does this entail? what does this mean? That the rifle has been re-proofed to nitro loads?
Well if so,as i believe so,surely this doesnt do a rifle originally made for BP any good at all? Or,can one find older hammer guns in .500 nitro?(3" case)

Just because a gun is a hammer gun doesn't mea it had to be black powder. Nitro powders came into being well (quite a few years) before Hammer guns stopped being made but it took a while for the proof laws to catch up.

I had a Holland 500/450 3 1/4" Nitro Hammer Double Rifle and I have seen a number of Rigby's.

Though when buying, it is wise to check that it is not just a reproof.

Hope this helps.

500 Nitro