Check out the French guns,many have three even four bites and most that I have seen have hidden fasteners. The French used hot proof loads as a sales pitch going as far as double and tripple proofs to show the strength of the guns. I do not mean that a tripple proofed gun fired a proof load three times what a standard proof load was however the load was usually up into the 32,000+ range. You should get a book giving you the proof marks and what the mean and the pressures I think one is titled The Standard Directory Of Proof Marks. I have the book in my shop and I will check the title and get back to you people if that is not correct.