FWIW
Just today I got around to patterning a 20 gauge nine inch barreled Howdah that I picked up recently. Since it's a short range affair I patterned it at ten yards this first time. I was favorably impressed. The patterns were very uniform, though wide. There was 60% coverage and even enough that it would be good enough for birds out to maybe 15 yards.
The load was 3/4 oz of 7.5s, 55 grains FFg (two drams), Nitro card, 1/4" cushion and OS card, Nice shooter. Horrible trigger.
The ten gauges must've been pretty fierce. But, then, so are tigers.
Pete