Sherman Bell's testing reported to Gauge-Mate in 2006
20g AA Super Sport 7/8 oz. now is listed at 1300 fps. I don't know about 2006
28g AA Target 3/4 oz. is 1200 fps
The reported increased velocity is presumed to be from less friction with the larger bore, and it would appear that the plastic wad effectively sealed the bore 12 to 20 and 12 to 28
In the 12-gauge gun with 20-gauge adapters:
A Winchester 20-gauge A-A Sporting Clays factory load of 7/8 ounces of #7 1/2 lead shot, fired in a Silver adapter, gave a velocity of 1319 ft/second and developed a pressure of 7700 psi. The same 20-gauge load fired in a Gold adapter gave a velocity of 1324 ft/second and developed a pressure of 7800 psi. With all 0-rings removed from the Gold adapter, per your request, the velocity was 1302 ft/second and the pressure was 7900 psi.
In the 12-gauge gun with 28-gauge adapters:
A Winchester 28-gauge A-A factory target load of 3/4 ounces of #8 lead shot, fired in a Silver adapter gave a velocity of 1247 ft/second and developed a pressure of 8300 psi. The same 28-gauge load fired in a Gold adapter gave a velocity of 1285 ft/second and developed a pressure of 8400 psi. With no 0-rings in place on the Gold adapter the velocity was 1255 ft/second and the pressure was 8100 psi.
A different lot of the same Winchester 28-gauge A-A factory target load was fired with Gold adapters. The velocity was 1318 A/second and the pressure was 8200 psi. With 0-rings removed the velocity was 1297 ft/second and the pressure was 7700 psi.
