There’s a .22WMR version, too. I shot a BIG rat with one right in my kitchen cupboard once.
The .22 WMR shotshell holds 70% more shot.
I thought Henry should have come out with their Garden Gun in .22 magnum.
The shotshells are only a little more expensive than the .22 LR, and should increase the effective range to 40-45 feet.
The energy on these #12 pellets drop off so fast, I doubt they would do much damage beyond that. At 20 yards, 60 feet, they are down to 502 feet per second.
At 15 yards, they are traveling at 604 feet per second.
I think you need the next size up, #11 shot, to be effective to 20 yards. At 20 yards, #11, starting at 1000 feet per second, would be down to 623 feet per second, with a 40% heaver pellet.