Fox Collectors

what type of ammo is preferred for the older SxS's? Are lead Shotshells avaliable at all anymore?

Lead Shot shells are alive and well. Some makers such as RST are producing ammunition specifically for older guns. However, without knowing what gun(s) you classify as old, what condition they are in or your intended use it is not really possible to make a recommendation. I do recommend you consult with a qualified gunsmith and have him inspect your gun(s) to determine the serviceability of the gun(s) you have in question and go with his recommendation.