Martin - you cannot shoot WW of anything in that .58 and expect accuracy with one exception. The slugs won't load as you won't be able to cut the lead with the lands, and with round balls, the patch will cut at the crown and powder gasses will cut them. For boar, pure lead will work just fine.
: Now, the only way to shoot WW balls in your .58 would ber to use a very grossly undersize ball, like a .562". That way, you could possibly use a thick patch to take the lands. You might be restricted in loading with undersize WW balls, ie: it will now allow as heavy a load as a larger pure lead ball with proper patch.
; A 260gr. WW round ball will not penerate as deeply as a pure lead 460gr. slug - highly unlikely, anyway - BUT - penetration should be more than needed, pure or WW. A pure lead .575" RB will make the off side of a bull moose (double lung'd) after breaking the leg bone on impact. That shoulh do for boar. .58 calibre round ball muzzleloaders were common "Bear Guns", made specifically for that purpose in the 1850's in the Western USA. "Califonia Bear Gun" was engraved on one make of them.