RE 20 gauge vs 12 gauge.
The recoil argument for 20 over 12 is becomes a moot point when you factor in 12 gauge mini-shells. 1-3/4 inch mini-shells are joy to shoot out Mossberg shotguns, single shot and double barrel shotguns. The bump in capacity is nice too.
If you haven't done so already, get a mini-shell adapter for your Mossberg or Maverick. This $25 adapter allows you to shoot both 1-3/4 inch mini-shells and normal 2 3/4 & 3 inch shells out of your gun.
This kit essentially provides a 590S conversion for your favorite Mossberg Pump-Action in a more robust design. It contains our patent-pending Universal Cartridge Adapter and low-drag no-snag Magazine Follower which allows smooth cycling of 1-3/4" Minishells up to 3" Magnum cartridges in the...
defendertactical.com
What about 410? I use a 410 single shot shotgun for killing squirrels that are chewing on my deck. The last one I killed I couldn't find my hearing protection in time and shot it without ear pro. I was amazed - no ear ring!!!
I kind of wish I picked up a Shockwave in 410. The 12 gauge Shockwave, is more or less a useless gun and would be all around more functional with a stock on it. I may get a stamp for mine in the future.