steel cased ammo in your Mini-14 should not cause any problems. Steel cased ammo has been used for years and by many different governments, including our own. The primers will not be damaged as they are not steel, just the case. The only way I could possibly imagine uncoated steel cased ammo hurting a chamber is if you got some crud or abrasive crud on the cases as they were feeding, otherwise I wouldn't hesitate to use steel cases. I use the steel cases S&B ammo in my 7.62x39s and have used it in my Mini-14 without problems. HTH. Mikey.