A break-open, single-shot, 12-gauge shotgun is the least expensive, most handy, versatile firearm that anyone can own. A subsistence farmer in the Third World or outdoorsman doesn’t want a heavy tactical shotgun. When on foot out doing chores you aren’t going to carry more than a pound or so of ammo.
12-gauge shells weigh 9 rounds to the pound. A box of 25 shells weigh about 3 pounds. This limits how much ammunition you will carry, because playing Rambo with your shotgun gets in the way of carrying mission-essential kit like shelter, water, fire making, food, first aid, navigation, communication,..survival! So, you take what you need for camp meat opportunities which may occur during the day and a few for two- or four-leggged predator deterrent on the walk home. If backpacking, you will carefully make that three pound box of 25 shells last as long a time as possible, especially if re-supply is a great distance away.
This is a simple meat producer, predator deterrent and personal defense gun. Low cost, safety, simplicity, ruggedness, durability, ease of carry, fast handling and versatility are its attributes. What other firearm can you get for about $100 used or less than $200 new which does so much?
The break-open shotgun “always works,” is simplicity itself and is legal most places which don't permit people to carry a handgun or military rifle. Minimal training is needed. You can’t “short-shuck” one, as often happens to novice “pump gun” owners. It keeps going like the Energizer Bunny with minimal care, despite rain, sand, snow, ice, mud, dust or saltwater exposure AND it takes apart to fit in your pack. Nothing much breaks on them unless you are stupid enough to dry-fire one with the action open and slam the action closed, breaking the firing pin.
A break-open single-shot 12-gauge with rebounding hammer and automatic ejector is the best choice. This is because 12-gauge guns and ammo are the most effective, least expensive, and available everywhere. A typical break-open single-shot weighs 6-1/2 pounds. Yes, its recoil can be intimidating. So buy low-base “field loads” and “low recoil” law enforcement slugs and buckshot to take the “sting” out of it.
If recoil shy, a 20-gauge gun may be considered. Its lighter shot load has about 10 yards shorter effective range than a 12-gauge, roughly 35 yards vs. 45 using a full choke barrel on game. Figure five yards less if using a modified choke and ten yards less if using a cylinder bore. Twenty-gauge guns and ammo are less common and ammo is more expensive. If you do buy a 20-gauge get one with a 3-inch chamber, which can shoot either standard 2-3/4 inch field or heavier 3-inch Magnum loads. A 3-inch Magnum 20 carries the same shot load as a 12-gauge 2-3/4 inch field load.
Forget shotguns in other than 12-ga. or 20-gauge if cost or convenience is a factor because the ammo is much harder to get and more expensive. A viable case can be made for the .410-bore because of the lower weight and cube of its ammo, but a .410 has VERY limited range, no more than 25 yards. The .410 slug only compares to a .25-20 rifle in energy. Thin patterns with only a half ounce of shot in the 2-1/2 inch shell and 11/16 oz. in the 3 inch shell make game hits iffy beyond 20 yards. This is because it takes about 200 shot in the shell to produce effective killing patterns for game the size of a rabbit or duck. Avoid shot sizes larger than No. 7-1/2 if possible with the exception of the 3-inch 5-pellet 00 buck defense load. It is more effective than the .410 slug within 25 yards and is whole lots better than no gun at all.
If you shop carefully you can find single-barrel shotguns which come factory fitted with an extra rifle barrel chambered for common rifle or pistol cartridges such as the .30-30, .357 or .44 Magnum. You might consider buying one of these if you already have a handgun or rifle in one of those calibers, but backpacking an extra barrel and ammo is absurd. But, it is OK to stash them in your 4WD, boat or aircraft...
While a smoothbore shotgun is no substitute for a rifle, most can place a slug about as accurately as a non-expert can shoot a revolver from an improvised rest at the same distance. Reality is being able to hit a 6 inch target at 40 to 50 yards. Having rifle sights on your shotgun doesn’t improve its inherent accuracy, but does let you “zero” the gun so it hits where you point it, in case your plain bead-sighted barrel doesn’t.
Short barreled shotguns with rifle sights are over-rated. Rifle-sighted shotguns are usually either improved cylinder choke or full open cylinder bore with barrels 20 to 22 inches long. While handier to carry when taken apart, shot patterns they produce are thinner and their effective range with birdshot or buckshot is significantly reduced. If accurate shooting beyond 40 yards is important, you should get a rifle instead! Ask yourself if it worth giving up 10 yards or more of effective game range, effectively limiting you to 25-30 yards, to get handy length and cool rifle sights whose benefit is mostly mental? For most people a 26 inch Modified choke is best on game and hits well enough with slugs for practical use. If you can learn to do the job with the plain vanilla gun you have, learn to love its Long Tom barrel and the virtues of instinctive point shooting.
Expert shotgun gunners wield a shotgun on moving game as if sweeping a paintbrush. The “non-expert,” single-shot user makes his one shot count by shooting his shotgun at game the same as if it were a rifle. Pot meat is sitting turkeys or squirrels in tall trees. In a REAL (not "play" exercise) survival situation sportsmanship goes out the window and "ground sluicing" birds is OK as is taking game out of season. But don’t try to take any wild game out of season and then tell Mr. Game Officer you were in a survival situation and did not want to waste the left over’s, so you brought them home after you rescued yourself. That dog will not hunt and the bird will not fly either!
Simplify your ammo supply. For initial training and periodic practice buy a case of “dove and quail,” or “trap” loads of No. 8 shot. For general hunting, predator control, big game and home defense buy 100 rounds each of “duck & pheasant loads” loaded with No. 6 shot, and either No. 1 (best choice) or 00 buckshot (OK) and 1-oz. rifled slugs. “Low-recoil” (reduced velocity) buckshot and slug loads made for law enforcement use are less punishing to shoot in a light gun. They give up little in effectiveness. Some guns pattern better with them than they do with “high base” loads, so it is worthwhile to seek them out and test a few if you can find them. Otherwise learn to hold onto your gun tightly, cut loose and get over it. The force of gravity is perpetual and that of recoil is brief, so enjoy the virtues of your simple and handy gun.
Advice for the basic load of 20 gauge ammo load parallels the 12-gauge. Buy a case of 2-3/4 inch 7/8 oz. No. 8 shot “dove and quail loads” for training and practice, then 100 rounds of 1 oz. No. 6 shot “duck & pheasant loads” for general hunting and 100 rounds each of buckshot and slugs for predator control and home defense. The 3-inch Magnum, 18 pellet No. 2 buckshot has better penetration than the 20 pellet No. 3 buck loaded in the 2-3/4 inch shell, so get these if you get a 20-gauge gun with 3-inch chamber.
Thoughts on carrying a personal weapon while traveling dangerous places which prohibit foreign civilians from possessing a handgun or center-fire rifle. If self-defense capability is more important to you than putting meat in the pot, then you want a gun which can be accessibly carried, concealed if necessary, which handles easily and can be quickly grabbed, instinctively pointed and fired instantly. Only a short barrel gun fits these requirements. Harry Archer and I once had to equip a married couple whose assignment normally wouldn’t have required them to be equipped with personal weapons, but the situation on the ground changed, and I had one afternoon before they left CONUS to train them. Harry brought got two H&R Toppers and made a quick hardware store trip for a tubing cutter, mill file and pipe deburring tool. They didn’t make the short barrel, iron-sighted “Tracker” or “Survivor” models back then. Ten minutes with common hardware store tools turned those 28-inch full choke barrels into 18-inch cylinder bores with a slight muzzle constriction induced by compression of the tubing cutter. They patterned 12 pellet “short Magnum” 00 or 16 pellet high base, or 20-pellet "short magnum" No. 1 buckshot wonderfully out to 30 yards. These legal-length sawed-offs stowed in a Fiat 124 between seat and door post and proved successful in thwarting a kidnap attempt by terrorists, whereas another less fortunate embassy employee was killed a few weeks after our charges returned safely home.
Any single-shot gun is a “shoot and scoot” weapon used only to provide an opportunity for escape. If you must use a shotgun in combat you must realize that an opponent who knows that you are armed only with a shotgun will change the battlefield conditions to his advantage. In an extended gun fight an adversary will undermine your use of the shotgun by staying outside its limited range and just plink away at you. He will get behind substantial cover capable of stopping buckshot, and expose little of himself for only brief exposures, being difficult to hit with a slug beyond pistol range. He will then rush you while you are reloading or extend the time of battle until you run out of ammunition. If reduced to using a single-barrel shotgun, you must quickly end the fight at close range, exploiting your shotgun’s strengths, surprising the bad guy who didn’t expect you to be armed, while you escape the killing field before an opponent can take advantage of your weapon limitations.
With practice you can learn to reload and fire more rapidly than most people would expect, especially if you carry spare ammo on an elastic carrier on the butt.