Fred,
Mine feeds a lot better with 357 than 38SPL, the shorter case can sometimes "jump" over the top of the chamber when feeding.
Regarding pressure well, I've shot 357 magnum loadings that are really hot using 180grn bullets with no ill effects at all so go for it! These rifles are stronger than pistols so any loads thats good for a pistol is OK in the rifle. You will find that the muzzle velocity is higher since you haven't got the pressure loss of a revolver & a much longer barrel. About 100-150fps faster is usual.
Enjoy it!