Ive seen ads for a few single shot uppers that attach to a AR15 lower.  Does anyone have one of these?  Or has anyone shot one?  I wondered how the lower would hold up to the recoil and how the accuracy was.  

Interesting.. I'd like to know too.

It would seems that strenghting the lower to handle the recoil would do the trick. That is if you buy the complete package with their lower recieve.

Def2

I don't have one...yet. Here are a few of the offerings out there:

www.mmag.biz

www.watsonsweapons.com

www.ferret50.com

server50.hypermart.net/50bmg/001.htm

Tackdriver:

I purchased a .50 BMG conversion from Darran Wardle of Advanced Long Range Systems in Oregon.  You can check out his website at http://www.50bmgar15conversion.com

I have to say that I am thrilled with the quality and accuracy of the conversion.  I am able to easily punch 1 MOA or smaller groups with decent ammunition (i.e., handloads or commercial match ammo).  Darran custom builds every upper to the customer's specifications.  The machining and finishing are top notch and much better than I expected.  

I looked at the other conversions available before I decided on the ALRS conversion.  The others may be just as well made, but I prefered a traditional bolt action rifle with an extractor and ejector.  Some of the other conversions use a removable breech block that requires the user to unhinge the upper from the lower for every round.  Also, I liked all of the design descriptions and information available on the website.  Everything stated on the site is true!

I built my rifle on a stainless DPMS lower with a Jard single stage trigger.  The stainless lower is not required and only adds weight.  It was just my own personal preference.  Darran says that any lower can be used without damage.  I scoped my rifle with a Weaver V24 in Leupold quick release rings.  So far, the Weaver is still in one piece.  I'll see if it stands the test of time.  It should, since the recoil is very mild (much less than a 20 gauge shotgun).

This is my second .50 BMG rifle.  My first rifle was a custom single shot shell holder type action.  It was built with a M2 barrel and lacked match grade accuracy.  The AR-15 idea was appealing since I aready had lowers and the upper could be shipped directly to me.  You may also want to check out the Ferret 50 at

http://www.1919a4.com/ferret50/

I hope this helps.

There are several uppers that attach to an AR-15 lower.  For a complete list check out www.fcsa.org and go to the visitor's page.  From what I have been reading in VHP (Very High Power, the FCSA's magazine) the AR-15 lowers are indeed holding up quite well.  You have to remember the brakes on these .50s are great and are extremely affective.  My Armalite AR-50 (not a AR-15 add on) recoils about like a light-weight .243.  The AR-15 upper that I have been very impressed with is from Ferret Arms.  It is a bolt action barrel and receiver that attaches to the AR-15 lower.  You do need to add a heavier hammer spring, but that is not a biggie.  The AR-15 conversions where you crank in and out the bullet/firing mechanism work very well and are quite accurate, but dear God they are slow.  That is where the Ferret shines; it is as fast as any single shot bolt action rifle.