Usually yes I have read. But I do not believe that this is that a d its not explained as that in company literature. This cherry is old as stated and started for a different larger caliber the 38 s&w. As that cartritage was eclipsed by newer its large dia was obsolete and re designing got it a S.Well, that is close. The "S" really means "size" at it will be at the largest diameter and made from a new cherry. The "U" means "undersize" the smallest diameter and made from a worn cherry, unable to be sharpened again. FWIW