I really shouldn't post this, 10ga shells and components are hard enough to find as it is. We are pretty much forced to handload for them now. I guided for 30 seasons and have killed and seen killed my share of birds. Where we hunt now we kill geese on nearly duck hunt. I always carry my 10 when we hunt the fields where geese are present. The secret to the 10 is to never shoot shot smaller than BB's and to load enough of them to achieve the pattern density required for long range. Velocity needs to push 1300fps. Guess it is bore size, but patterns with big shot just hold up better than with any 12. while the 3.5" 12 looks good on paper it just doesn't cut it in the field compared to the 10. It's not even close. Anything that can be killed or even crippled with a 3.5" 12 will be absolutely crushed with a 10. Advertising and gun writers spewing propaganda about HV and low payload weights are killing birds best shot with a 20ga. They are in the business of convincing folks they are fantastic, while the ammo manufacturers increase profits by lowering the most expensive components in the shell. Most of that excess velocity is actually shed in the first 10 yards. Round pellets, drag etc, make it useless. Bring a LRF and hunt with me. You will not believe how far a 10 can kill light geese. As for the 12, I have around a dozen of them. Shells are cheap and easy to find and I carry one sometimes with 3" bismuth. 3.5" shells will blow the pattern if you choke it tight enough to justify the purpose of them in the first place. More often I carry a 3" 20 loaded with Tungsten 4's. The 20 will kill ducks as far as any 3.5" 12ga with steel. It does a good job on light geese that are actually in shotgun range. You just have to hold tighter because the pattern is smaller. Actually makes it more fun. But if you have Canadas around and would like to see them fall dead instead of flying into the ground there is no choice other than the 10 with proper loads. Shooting over decoys you can literally make it rain Snows. All the propaganda and wishing in the world will not change this fact.