Not .223 but 7.62. I've had rounds stored on stripper clips made of identical materials to those used for .223 for over 10 years with no problems. I've opened properly stored .303, which has a different stripper clip design, after 45 years with no issues.
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”