Some work fine and some do not. It all depends on the quality of the particular receiver casting and finishing and the quality of the surplus parts use for the rest of the assembly. Rifles with bad receivers or poor parts or a combination of the two will mean function problems. If you have a good one that functions well count your blessings and enjoy it. If not, they can probably be difficult to diagnose and make reliable. Dangerous? Not likely. Thousands and thousands were made and sold and I doubt any blew up....although many may have never functioned well so you don't see many in service anymore.