I recently came across a heavy barrel ar-15 barrel for $10.  The only problem being that the front sight was striped, it was missing the delta assembly, the barrel extension pin was grinded off, and the barrel nut was cut in half.  I bought all of the parts I needed to put in on my upper except for the barrel extension pin.  I was able to attach the barrel assembley to the upper with a good alignment.  What I need to know is:  will it stay in alignment?  I thought maybe it would with the continual movement of the bolt into the barrel extension, but I wasn't sure.  Will the barrel rotate with use?  Should I just replace the barrel extension pin and if so how do I go about doing it?  If I do this should I remeasure the headspace?  Should I replace the entire barrel extension (I don't think so but I have an extra so I thought I'd ask)?  What should I do?   Is it safe to shoot right now (everything is set up and the sights seem aligned, it could drift though since the barrel extension pin does not hold aligneent in the upper reciever).

Thanks for any help,
Fred

I'd replace the extension pin. Beings how they ground it off you may be able to drill the old one out with a drill press and the correct size bit and tap a new one in. If you change barrel extensions you'll need to make a tool from an old bolt head or buy the special socket from Brownell's or a supply house and have a very good settup to hold the barrel. Also headspace and gas port location will possibly change with a new barrel extension installed. Myself I'd drill the ground pin out and tap in a new index pin being carefull not to drill to deep. A good drill press will have a depth stop. Index pins are real short so it won't reqire much, just make sure your centered up when you start and use the correct size bit.

Thanks for the help.  I will try drilling it out on my press first.