Am interested in getting an M4 upper, but I wonder about how well a Detach Carry Handle would hold up, especially under combat conditions. I know that sounds silly since I probably won't be seeing combat soon, but it is a military rifle. Also, how well do these things hold their zero after taking it off? Just how durable are these things?

I have never had a problem with one, but you really need to crank the knobs down with a screw driver, rather than just hand tightening them. Also, make sure that you take the slop out of the rail by moving the handle foward until the cross pins contact the edge of the channel. If you don't, during recoil the handle will creep forward. I don't have much experience in .223 guns, just the big bores, so it may not be such a problem with the smaller pop guns. Keep in mind, the handle opening is also much smaller in the detachable handle than in the standard A2 receiver, so if your hands are big, you may have trouble using the handle to carry the gun. Most people never use the handle to carry their gun like a suitcase anyway........

I read a post from a guy on the Armalite site a while back who said Armalite handles are good handles, they fit and are of good quality. They cost more than some cheap knock-off. He said the one he got from Bushmaster was not a good piece of work, I don't know, just passing along info.

I'd say a quality detachable handle is just as durable as on that was forged as part of the upper. Ditto Tony's remarks about pre-loading it forward against the rail channels. My Bushy handle is first rate, but then again I got it 7 years ago so I can't comment on the current quality (I have also heard some horror stories). I don't think I would use a handle mounted scope on one since you already have a rail right there anyway, and on the handle it seems like it would be susceptible to shifting from recoil. Forgot to mention, mine returns to zero perfectly when reattached. Just make sure it's tight.