*How is it different than the Armalite AR10?*
There was a pretty good picture of an Armalite upper on a DPMS lower somewhere on AR15.com awhile back.
The double radius on the rear of the Armalite upper is replaced by a single radius like the AR15 on the DPMS.
The Armalite upper fits onto the DPMS lower, but there is a gap between the upper and lower at the diagonal between the two curves at the rear of the upper.
It doesn't look like a DPMS upper would fit on an Armalite lower.
I'm not sure exactly what the DMPS radius dimension is.
If thats about a clear as mud, I'll look for the picture and link it.