It looks like it is for an octagonal barrel. A Greyhawk has a round barrel. Also all Renegades, .54 Hawkens, .54 White Mountain Carbines, .58 Big Boars, all are 1" across the flats. .45, and .50 Hawkens, .50 White Mountain Carbines, are 15/16" across the flats. You need to know which size octagonal barrel this sight fits.