I still have the 5k sleeve that my primers came in, so I'll check. It would be interesting to find out if there is any functional difference between the KVB-556M and KVB223M such as cup thickness or primer composition.
Without anything more scientific than a "residue test" on my Lee Pro1000 priming system, the Wolf primers seem to be loaded with a Lead Styphnate compound (yellowish dust).
I know the Federal GMM primers still use Lead Styphnate as the priming compound as they can control the "flame" better than the newer "green" PETN priming compound. If the Russians never transitioned to PETN that would explain why their primers are providing "match grade" performance by comparison.
Machine guns are awesome until you have to carry one.