FORT has been producing a pistol in 5.7x28mm for a couple of years.
Yesterday on the reibert.info forum a brief notice was posted by KUGEL (one of the forum moderators) with a photo showing the headstamp of an empty 5.7x28mm cartridge case produced by FORT, headstamp = ФОРТ 5,7х28
Kugel points out that the cartridge case is brass plated steel.
Photo posted by KUGEL-
Link to the reibert.info page: https://reibert.info/threads/patronnye-novosti-ukrainy.638672/page-11