The grind is a real factory's fuckup. You guys are getting the export versions of saiga where such things are quite rare. On the local market here in Russia it's a real problem. 50% of all saigas from the factory are having something like that.
It was a nice joke from the Izhmash several years ago. A man bought a brand new S12 from the local dealer. Being quite a busy person first time he tried it was a year after. He tried to arm it, but nothing has happened. The shell didn't go into the chamber. He removed the cover and ... everyone was totally surprised to see that his S12 has no chamber!