Again, the internals are similar, though the current semiauto AR-180b uses an AR-15 type configuration of a stampred upper receiver with gas piston-type action, plus a polymer lower receiver and trigger mechanism housing. Accordingly an AR180b, while a great little carbine in its own right [I've had examples of the earlier AR-180 model with folding stock as produced by both Great Britain's Sterling Arms and the Japanese Howa machinery company] would be a little more complicated starting place for a XM-8 repro...hmmm, XM-8, SL-8...Almost as if they've had this idea from the get-go.... And the current AR180b is also arranged to use M16 magazines. Accordingle, it realy looks like the SL-8 is the better place to begin.
My only complaint with the SL-8 (and I'm sure many other civilian shooters shared this gripe) is its butt-ugly stock with that "butthole" pistol grip. If you're asking a buyer to pay out $1500 for a rifle based on a military design, you simply have to do better than that, IMHO. The SL-8's failure on the marketplace was undoubtedly aided by this.
It could have been issued with a proper pistol grip, too. They only would have lost the opportunity to sell it in California and New York, which probably wouldn't amount to all that many sales, anyway, as dedicated buyers in those states have a way of finding what they want elsewhere.
I often wondered why manufacturers of semiautos left the barrels "slick" after the ban, when a simple lathe job would have yielded a "muzzle device" which had at least the proper "look" to it.
To me at least, a semiauto lookalike just plain looks strange and incomplete without a muzzle device of some kind.
Also, it demonstrates the utter futility of the Ban, when industrious, independant, and ingenious Americans go to work on the problem.