Converted from semi-auto? I am thinking it is one of the Numrich semi-autos converted to full auto and registered when that was still legal.
Those are pretty rare, but I think the price would be in range for that gun. Just make sure the seller has the papers and the gun will transfer on a Form 4.
(It could be an original Model 1927, but anyone who would convert one of those would be a barbarian, since they are considered machineguns anyway.)
Jim