Are the Colt and LMT carry handles essentially the same? I just bought an LMT upper; would the Colt carry handle fit on it?
Yep, they are interchangable.
I have Rock River and Bushmaster carry handles and they are all inter-changeable between rifles. Only problems I have ever personally seen was with one of my Bushmaster uppers didn’t like to mount the Rock River handle easilly. But I just leave the Bushy handle on it and it’s all good.
This is not accurate. While BM and RRA are interchangeable with each other, their handles are made for the (incorrect) height front sight bases they use, and are not interchangeable with manufacturers that use the (correct) height front sight base.