The Single-Barrel, Break-Open Shotgun

[Timelord]

The benefits of a double outweigh the slight weight increase. For self defence the double is by far the more effective and no attacker would risk any sudden aggressions in front of two barrels. Also for multiple attackers it is far more effective and that has a high probability in some scenarios. You can load one barrel with shot and one with heavy shot or slug.
What is not pointed out in Charles' comprehensive narrative is that slug can not safely be fired from any barrel with a choke tighter than half choke (improved cylinder)
A two barrel "over and under shotgun" in a scenario WROL is easily cut down to a handy pistol sized weapon of immense "fight stopper" firepower and is probably better than any other for close quarters SHTF defence, especially used by a non expert! Supported by other weapons, firearms, manpowered projectile or hand to hand, then it is a formidable and confidence boosting set up. The rate of fire that can be sustained by a twin barrel ejecting shotgun is substantial and will exceed that of a 3 shot UK section 2 certificate pump gun for 99% of people.
Now - two identical guns, one cut as a pistol in an expedient holster and one still as a 26 inch plus barrelled shotgun, both firing the same calibre and with commonality of parts, would be a desirable prepper weapon set for most situations that may require that level of force. Yeehaar! (Don't forget you need the ammo as well and possibly the ability to reload it)[/i]