The 64 is used on 1813 and later versions of the single shot target rifle. The 54 is viewed as the "sporter" version, and not the target version. For Olympic style shooting, the 64 action is the way to go. It has a removeable baseplate to convert to biathlon style shooting (with a magazine), but the majority will be single shot with the stainless baseplate. The 2013 and later actions went to a square action with a changeable barrel system and shorter barrels with bloop tubes. The 54's will be significantly cheaper than the 64's.