I think I found what the silver thing is... A concho? I think it is for a saddle. The bell still has the ball inside. Any help on this monster bullet or the flask looking thing with the two holes?
The casing is too corroded to read anything. You are correct in that it appears to have a nylon or plastic tip. Not knowing much about these types of bullets, why would it have this type of tip ?
Looks like a 22-250 to me. It is a modern round. The ballistic tip is basically a piece of hard plastic inserted in a hollow point. Upon impact it acts like a hollow point. With the insert the round flys very flat and long.