2oz should be an almost "square" load - isn't it?
That sounds about perfect to me.

I had a friend, now gone, who used a 6 bore SxS percussion ball and shot gun for the trap portion of the turkey shoots he attended. This SxS had 36" tubes and weighed about 12 to 13 pounds. Once started, you couldn't stop your swing if you wanted to.

He'd sent the gun to H&H, for "re-furbishing" and they returned it, in lovely shape, as a 5 bore - the bores gleamed brand new.
Wil punched out his own wads - donna-conna and cork & heavy card stock.
He used only 2 to 2 1/2oz of 8's and just pulverized the birds. I think, maybe 5 drams 1F.

I found this on 8 bore loading.

"The Dixie Gunworks catalog has a lot of data on the old guns in the back. 270 grains (9 7/8 drams) is the Defintive PROOF load. The Provisional Proof is 394 grains (17 1/2 drams). No wonder they fired them by remote control in an amoured room.

The Service load is 135 grains (4 15/16 drams) and a 763 grain ball or 1 13/16 ounces of shot. Wonder why they cut it to the 16th ounce on the bigger gauges when they didn't on the smaller ones?"