Most powerful 20ga slug?

[50caliber123]

I just had a range outing yesterday with a friend and his Pardner Pump 20ga. Since he has a 3" Chamber we decided to find the 3" 1oz Brenneke and try it out at 25yds. With just a bead, accuracy is pitiful, especially since it shoots them way low. However, I never seen such a monster load out of that gun. Reminded me of a 12ga slug in terms of blast and recoil. Is there a more powerful slug load available for smoothbore barrels than the Brenneke magnum?