Ciarog said:
How much momentum can one be expected to block using the force? Most shotgun gauges have a muzzle velocity between 1,100 and 1,350 feet per second (335-410 meters per second). A 12-gauge shell will generally throw over an ounce of lead in the air and most automatics hold five to eight of them, all off which can often be fired off by a skilled shooter in little more than a second. Anyone getting hit by all that metal at ranges below 5 rods or 25 meters ain't gonna be in much condition for swordplay.
Okay, just to humor you, I did the math and...
There is a reason why they use very small objects at high speeds in guns. That is because of the effect described in Newton's Third Law of Motion. Once object A acts on object B, object B acts with the same magnitude with opposite direction on object A. So accelerating all those pellets with a combined mass of about .0378 kg to 410 m/s (at the max of the range you noted) in, say, a tenth of a second is about 154.98 N of force acting on the shell. Take that and divide it by a 150 pound man (using 68 kg for consistency of units) and you get 2.28 N of force acting on the person which will induce a speed of about .2279 m/s on that person.
Just think about that, if a fly splatter-died against the windshield of a bus having a mass of 1000 kg (just for shit's sake) and it weights less a few grams, then the equation F = ma would look like:
(MASSIVE NUMBER)a1 = (tiny number)a2
and would even out to a very tiny a1 and very large a2 so, essentially, the same force that will more than murder a fly will effect a miniscule acceleration on the bus' part.
The same is applied to the whole gun-thing in that we don't frequently fire things that will send us flying back at immense speeds, so we can't imagine that our foes would be flying back at immense speeds and our projectiles won't have too much force behind them save for their shape which- against some ethereal force- doesn't matter.