When SHTF most problems will be less than 50 yrds with a possibility for longer ranging. You must absolutely be proficient at the distances under 100 and have the tools for that.
I am comfortable with bolt action if needed but prefer a semi .308 or greater with a muzzle break to reduce lift and assist with getting back on target.
Comfortable with revolvers with speed loaders for 25 and under. I just like the reliability and I breathe and Aim. I don't send a lot of rounds out as I am focused on going through the target. Always shoot at the chest and continue until they stop. A good semi like a Kimber will provide excellent tool here.
All around for 50 and under with very little practice is the 12 gauge with double 00 buck. Make sure the barrel is 18.5 inches, to stay legal and provide accuracy. Couple of hints, 00 provides at least 8 pellets in one shot. Prefer 2 3/4 most economical and the least kick of the other sizes. Will accomplish the same task. For crowd control you can shoot the concrete at 15 degrees and take them out the legs or shoot the closest one by focusing on the front bead, in the chest. don't worry about the back sight if you are inexperienced and haven't taken the time to learn to shoot properly. With 8 shot coming out at 15yrds you will hit the target and anyone to the left or right.
The pattern diameter with my 18.5” cylinder boar Mossberg is about 3.5 inches at 15 yards with a 9 pellet, 00 buck, 2 and 3/4” shell.
With a 15 pellet 3” magnum round it’s about 4.25 inches.
I’ve measured it. I’ve tried a variety of ammo brands. Cheaper ammo tends to give a slightly (very slightly) larger pattern than good stuff. There is NO WAY you are going to hit people on either side of who you are shooting at with an 00 buck load at 15 yards.
Contrary to popular belief, you still have to aim a shotgun. pattern spread is not substitute for practice and proficiency.
Anything over 30 yard, get a rifle.