Any shotgun is about barrel length.
At 20 paces the number 7 is probably about a 6 foot diameter on a long barrel, and on a three inch barrel, it's about 12 feet.
To do any damage with number 7 shot, you've got to be within 20 feet.
Hey, you've got an old Louisiana squirrel hunter here. :) I grew up shooting a H&R 20 gauge topper junior, model 490, with a modified choke. It still sleeps less than 6' from me, every night. :) It was a gift to me from my dad when I was about 8 yo. My favorite shot is 7-1/2. With it, I've killed truck loads of squirrels at well over 20 steps and ducks as soon as they lock up. On a covey rise, back when we had quail in Louisiana (before the fire ant invasion), I usually knocked down at least two by carrying a couple of shells in my hand.
A rifled barrel spins the shot and causes it to spread greatly soon after exiting the muzzle. A smooth bore shotgun doesn't have that problem.