Forced,
I have drilled 1/4 inch holes in the receiver to allow for new rivets to be used. I used a new Titanium Nitride bit, the bright yellow kind, and cutting oil. I have two receivers and I got two holes, of the 4, drilled and they chirped and squeaked but the drill press pushed them through making the appropriate spiral shaving. On the third hole the bit stopped cutting. my first reaction was that I had found a "hard spot" in the second receiver. Got a "new" hi-speed bit chucked and it dulled in just a few turns. These receivers are very "hard" as i got them. A pleasant surprise.
Thanks for your answer.
John