The choice for preservation some years ago was polyethlene glycol. It was poured into a long tray and the item was immerseded in it until replacement and sealing took place. Time in the tray depends on the item and its fluid content. After stabilization a wax preservative was applied to seal the surfaces. Poly used to be carried by a good hardware store and may still be. Chemical supply houses would have it.
The idea that there may be more material in the area that you found the gun is a good one and should be followed up on. For this, contact the local university history or archaeology department. They could conduct a survey of the bottom and send down divers to look for posssibilities. This could be an isolated find, or it could be a sunken boat owned by Indians, or even voyageurs. In any case, it is a great find and rivals anything I have seen recovered on land, or in the sea.
Dick
