I think the 58 rb is the ultimate rb caliber hard hitting, accurate, and at 1800 fps as flat shooting as 54.
Depending on how heavy a gun you want, you could take a T/C Renagade and rebarrel it for 58 cal. They are 1 inch barrels. There is a Renagade stock assembly for sale on http://www.dream-tools.com/tools/mes...hiptradingpost Maybe this will help, then you could put barrel on for probably $200, not sure if stock assembly comes with lock or not. With 32 inch 1 inch 58 cal you would be looking at 9 lb gun, good weight in my opinion considering recoil. I have a 1 1/8 36 in 58 hawken, I built from TRACK OF THE Wolf kit, that weighs 11.86 lbs, fantastic shooting round ball gun, fully capable of accurate 1800fps. Hope this helps, I have several guns on the drawing board, otherwise I would offer my services.