Anyone here have an AR in .50BMG?  I am thinking about building one.  Are any of them worth it or should I avoid them and buy a bolt action .50BMG?

The Watson is excellent albeit horribly slow to reload.  The Ferret Spider is also a most excellent bolt on upper to the AR-15 platform and being a bolt action single shot as fast to reload as any.
My own preference though is the Armalite AR-50, which as you probably know has nothing to do with the AR-15 type of rifles.

ETA:  There is a Ferret .50 BMG upper for sale on the FCSA members only BB classified ads right now for $1650 but you have to be a member to access the members only BB.

Quoted: The Watson is excellent albeit horribly slow to reload.  The Ferret Spider is also a most excellent bolt on upper to the AR-15 platform and being a bolt action single shot as fast to reload as any. My own preference though is the Armalite AR-50, which as you probably know has nothing to do with the AR-15 type of rifles.

+1 on the AR50. If your going to shell out the dough, go ahead and get a complete gun. The AR50 rocks. It is also very accurate for a "off the shelf" gun

What about a Cobb50?  They are pretty damn cool in my book, and if I had the dough and the desire I would buy one...

http://nas4.atlanta.gbhinc.com/GB/044408000/44408310/pix3856060265.jpg

I have a Ferret .50 upper mounted to a RRA lower.  I love shooting it and it is plenty accurate.  Sucker is heavy, though.  The only problem I have now is finding a range in the Augusta area where I can shoot it comfortably.

www.ar15.com/forums/topic.html?b=6&f=3&t=195212