What is a stripped lower receiver on an ar 15?

I recently bought a Bushmaster 6.8 AR-15 and was wondering how could you tell if it is messed up?

• I recently bought a Bushmaster 6.8 AR-15 and was wondering how could you tell if the previous owner i bought it from messed it up. Heres the story i bought the AR 15 from my cousin and he was telling me a story where he accidently fired a 7.62x39 in his .223 AR 15 by accident. I was wondering if he did the same to mine but he said no and i was wondering how could you tell if he did fire a 7.62x39 in mine by accident also. Would the upper receiver be totally messed up or would there be extreme wear marks or what. I havent fired this rifle but i have cycled a few 6.8 rounds in it and it cycles fine very smooth and everything. Please tell me how would i know and if i fire it and everything works fine does that mean its perfectly fine and nothing i should worry about in the long run.

• Answer:

  Your gun is probably fine, although your cousin is an idiot. If you fired the wrong kind of bullet the chamber would definetly be damaged.