You seem to be equating longer shot column in the shell to a longer shot string. Even if that is so there's nothing you can do about it. The shot string, however long it is, is moving much faster than the target. If you miss in front with the first pellets in the string, it's not likely the target will run into the last. If you miss behind you'll miss with the entire string.
If you're using the same shot load with 12 and/or 20 gauge, I'm with Mike on thinking the difference will be negligible. The only significant difference will be the recoil, assuming the 20 ga. gun is considerably lighter in weight. JL

> Jim Legg <