12 x 70 means that your shotgun is a 12 gauge and has 70 mm (2 3/4") chambers.
65 MPa is the maximum mean value of gas pressure produced by the shotshell. This rating is typical for a shotgun with 2 3/4 " chambers.
You can fire any standard factory produced shells as long as the lenght does not exceed 2 3/4" (70 mm).
You should not use Magnum (3 ") shells with that gun.
For slugs, use chokes that are not tighter than Improved Cylinder.
Most IZH-43 (SPR 220) shotguns nowadays come with 3" chambers. Your gun is probably an older one or it is one of those short barreled coach-guns that come with 2 3/4 chambers.