11,7x53 AMP or 11,7x55 USSP


I have ammo named "11,7x55 USSP Subsonic Sniper XPL for Bavarian police"
Is this same as 11,7x53 AMP and what is story of caliber?



This appears to be the same case as the original 45 Blaser. What I have on this topic is mainly from Peter Petrusic:

Note that Early promotional images of the 45 Blaser show a lower shoulder starting c35-36mm above the base (much like the 425 WR case) whilst Romey sporting production specimens have the shoulder higher at c40-41mm. The first version with the lower shoulder appears to be the same as the no hs cartridge identified as an 11,7x55 Silenced Police Rifle for Germany, loaded by Romey for AMT - the firm of the former chief of ERMA.