6.5x53 & 6.5x54 MS


I have had both the 6.5x53 Mannlicher-Schoenauer and the 6.5x54 MS, both by Norma, both with 156gr. soft point bullets,for years. The actual case lengths are 53mm and 54mm. What is story behind the two case lengths? Is it like the 7.62x53R and the 7.62x54R in Finland, which, as I understand it, is a way around civilians not being allowed military calibers, so they just shortened the case 1mm?