A .223 is regularly used to drop caribou in the arctic and it’s more than adequate for killing a deer, within it’s range parameters (<250 yards). Some of the hunting bullets they have for the .223 are superb. I find it interesting how many people call it a ‘mouse gun’ with over 1200 ft/lbs of energy while the same crowd often talks about the .45ACP with about 1/3 of that power like it’s a death ray. The .223 is legal for deer hunting in 36 of the 43 states which allow high velocity centerfire rifle calibers for large game hunting.
I don’t use .223 nowadays for large game hunting because I’ve consolidated my ammo calibers down to a minimum. In this heavily wooded, coastal area, .223 doesn’t really offer me any real range advantages for hunting over a scoped, rifled 12ga barrel with sabot slugs, which itself with modern barrels and ammo has a 200 yard reach. A .50 sabot round out of a 12ga has ballistics similar to a .45-70. Even a 200 yard shot here is rare and often a homemade, cast lead Lee slug fired out of a smoothbore is more than adequate.
A .22LR is a seriously underestimated caliber in what it can do and it’s one of the few calibers I have kept in inventory. However, for much of what it does it’s often overkill. For much of what a .22LR is used for, a good air rifle can often do the job as well at a fraction of the cost. An air rifle is also safer for anything in the neighborhood when firing up at targets in a tree. An air rifle is also not a firearm in most of the USA and can often be legally fired within city limits. My preference is for a .22 caliber air rifle that does at least 800fps. An el-cheapo .177 Daisy 880 from Walmart is still more than adequate for squirrels and it can kill a possum, plus it’s very quiet. The Crosman Destroyer EX pellets from Walmart are excellent.
All said and done, there isn’t much that you can’t get done with a 12ga pump shotgun and an air rifle. Earlier in the thread it was talked about the .410 shotgun. With a $25 drop in adapter, a 12ga pump shotgun can be used as a .410 single shot. Adapters can also be had in other gauges and calibers like 20ga. I keep a .410, a 20ga, a rifled .22LR, and one in my primary handgun caliber.
The 2-3/4″ rifled .22LR from GaugeMate works in a pump (the 2-3/4″ ShortLane rifled .22LR won’t due to bore offset). It’s not a replacement for a scoped Ruger 10/22, but it’s ‘minute of rabbit’, so it’s adequate for what it’s needed for. It’s accurate enough to consistently knock around a tennis ball at 25 yards. Don’t even bother with the .22LR adapters that are smoothbore.
All in all, the 12ga is the most versatile shotgun gauge, and it’s the cheapest due to scale of economy in manufacture. It’s also very easy to reload 12ga, and even make the components for it if need be. A 12ga shotgun is also one of the only modern firearms where you don’t lose much performance if you have to reload your shells with blackpowder.
A 12ga is about as efficient with modern smokeless powder as a .223 but operates with 1/2 the chamber pressure of a .22LR. Many of the powders you can use for reloading shotgun shells are dual use, which means you can also reload your handgun ammo with them.
A shotgun is the one weapon who’s ballistic characteristics changes dramatically with a change in ammo load. With a change of ammo you can go from harvesting birds and rabbits to dropping a deer or defending yourself.
Barrel length isn’t that relevant with a shotgun since most of a load’s velocity is gained in the first 10 to 14 inches of barrel. Changing your chokes and having adequate sights matters more. A good, tight choke, like a full or an extra-full (turkey) choke, allows for usable buckshot patterns much further out than a cylinder bore choke does.