I haven't been able to find a double gun associated patent issued that date -- May 12, 1891. At least it is a date that U.S. Patents were issued. I thought at first glance that it looked like maybe a "trade" version of a Forehand, but on closer examination they were bolted by a notch in a deeper rib extension and this gun has underbolts.

It comes closer to matching the "Chicago Long Range Wonder" pictured in the 1902 Sears & Roebuck catlogue, but still is not exactly the same.