I got the M500A-RD delivered from Brightflashlights.com yesterday and mounted it. Because of the gooseneck mounting setup I have and because of the larger diameter of the Surefire forearm, I had some contact between the sight mount and the upper forearm piece. I remedied this with about 15 minutes of careful work with my Dremel tool. I can now slide a sheet of paper between mount and forearm so all contact between them has been eliminated. Just a heads up for those of you out there with a similar gooseneck mount on your A2; if you don't want to do a bit of surgery on your brand-new M500A, then you'll need to change your mounting system. Part of the upper half of the Surefire forearm is damn ugly now (I used a small grinding wheel to make a "trough" along the top of the forearm for the mount to ride in), but it's also completely hidden by the mount. Actually, I think it's kind of neat-looking because the forward portion of the sight mount is
so close, riding in its groove as it is, that it looks like it's all one piece with the forearm.
Here's some pics of the carbine sporting its new weaponlight.