FYI, CZ 452 prototype for 5mm is sitting in the Czech Plant but it's not finished. No due date per CZ contact.
Tech Tip on the Rem 591M plastic mags tending to have the new Centurion rounds hang up. There is a rather quick fix that seems to work for me. Use Medeco or Assa dry lube (obtainable from your local locksmith). This is a aerosol spray that you spray into the bottom holes of the mag while holding the mag upside down. Use it sparingly. Allow the lube to dry for approx 30 minutes and it will leave a fine white coat of lubricant on the inside of the mag. The hanging rounds will stop. This lube is used on high end lock cylinders. It works wonders on your household locks when you find the key becoming difficult to insert into the lock. Typically, this happens during temperature and moisture transitions in the Spring and Fall. The lube will not attract dust and dirt like other lubricants.