While I didn't stay for the Handicap, I did attend the 2013 Grand American at Sparta last month. The preponderance of competitors used O/U's, with some single barreled trap guns. Perazzi, Beretta, Guerini, Kreighoffs, and Citori O/U's were seen most often. Some BT-99's. But also a wide variety of other shotguns including Blazers, Model 12's, some semi-auto's, etc.

I don't know what shotgun the winner used...