You opened quite a can of worms, IME. I own many rifles, but only one shotgun. A mod. 101 choked IC and Mod. my wife bought for me 44 years ago. The gun has done everything I`ve asked it to do...and it shoots exactly where I`m looking. In other words it fits me, and it shoots straight. I learned this, as MD always says, years ago when developing loads for pheasant, and grouse. A 4`x4` cardboard was set at 25 yrds with a aiming spot marked in the center. A friend and I shot many various hand loads from 12 guages at these 4x4`s. Mostly 1 1/8 oz. 7 1/2 or 8`s for grouse and woodcock here and 1 1/4 oz 4`s and 5`s for pheasant. One thing we noticed off the bat was the 4`s and 5`s shot a tighter pattern at 25 yrds than did the 7 1/2`s and 8`s out of the same choke, in my gun, the IC. The other thing we noticed was my patterns were always centered, his gun threw the patterns about 1 1/2 foot lower than his POA. Consistently. Up to that point, we`d thought all shotguns shot straight...wrong. My friend was having problems hitting birds, not because of pattern density, but because of where the majority of it was going.
If it be 25 or 40 yards, make sure your patterns are centered.
