Are the .50 bmg uppers for ar-15s any good.  Do they pound the ar reciever to death.  What are the pros and cons.

I have a Serbu, but a friend is thinking this might be a good way to go.  But we all know the saying, buy cheap, buy twice.  So are these worth it.  (I don't see him putting too many rounds through it)

Check out the ALRS upper.  www.50bmg.net/index.html
The owner/maker just took first place at Raton.  I still may get one of these.  Some say the added spring for the hammer puts stress on the pins, some say it doesn't do a damn thing.  Ask around on Biggerhammer, lots of members have upper conversions.

pros- cheap, lightweight (sometimes), versatility, no paperwork!
cons- some don't offer loaded shell extraction, requires changing or adding hammer springs, stress to lower if you really think it does.