Watman, its not that your 52 has a loose chamber.  Much of the ammo out there in 7.62 Tok is really, REALLY hot loaded, its submachinegun spec for shooting out of PPSH subguns and various Czech subguns mostly built on the Beretta PM12 pattern.  Also, the caliber has a crimp design that is unique, its basically peened in three spots instead of a roll crimp or a crush crimp.  In almost any other gun I would tell you that a split casing is a huge red flag that you have a headspace problem or something equally significant, but in the 52 its just another weird quirk of this gun and its caliber.  Not to worry, keep blasting away.