I shoot a old M1 that has several barrels. When I bought the gun many years ago I got it for turkey hunting so I chose the 24" barrel. A few of years ago I bought a 28" barrel for it specifically to shoot crows and pigeons.
I have patterned the gun with both barrels and and the patterns are about the same with a modified choke. Point of impact is about 60/40 on both guns with the pattern being just a bit above point of aim but I shoot the gun better with the short barrel every time. My percentage is always better with it.
I don't know why. It makes no sense.
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A SUPER 90 and a crow in range, life is good. A good sandwich and bag of M&Ms doesnt hurt either.
Last season I employed a pair of M12 Heavy Ducks, both with solid ribs. About as heavy a 12ga pump gun as your going to find. The main gun had been cut to 24" and threaded for chokes. The back up was 30" full. Mostly had a modified tube in the main gun and used the back up for long passing shots. Couldn't say which one I shot better. I'd say Bob's right, there's something about the shorter barrel that agrees with you.
Some time ago I learned that barrel length has little to do with pattern density. The choke makes all the difference. Spent a good part of my life not knowing that.