[MYTH #1] Steel patterns poorly through a Full choke. The idea that steel shot patterns poorly and even shoots "blown" patterns through a Full choke arose, in part, because large pellets—BBBs, Ts, and the like—often do pattern very well through open chokes and because manufacturers discouraged the use of Full chokes in the early days of steel for fear of barrel damage. However, almost any load of BB or smaller steel will shoot tight, deadly patterns through a Full choke and won't harm choke tubes, either.
[MYTH #2] A long shot string helps you break targets and hit birds. A trapshooter at my gun club explained to me the other day how to hit the wide left and right targets from posts 1 and 5. "Just shoot way out ahead of them," he claimed, "because your patterns string out so long at 40 yards that the target runs into the shot"—as if, say, your shotgun were projecting an asteroid field into the path of an orange flying saucer. Although the pellets in a shot load may stretch to a 10-foot-long swarm at 40 yards, they're all traveling over 400 mph, during which time a clay target or bird moves only a few inches. A long shot string provides only a minuscule added chance of hitting a moving target if you shoot too far in front—the rarest reason for a miss.
[MYTH #3] Small gauges shoot tighter. "I've shot 10,000 quail in my life, most of them with a .410 bore," an Arkansas bird hunter told me once. "A little gun like that shoots tight as a rifle." The truth is that pattern spread is entirely a function of the choke in the barrel, not the diameter of the barrel itself. You can prove this to yourself on a sheet of paper: Shoot a 12 and a .410 with the same choke and you'll see identically sized patterns. The difference is that the 12-gauge pattern will have a lot more holes in it, which is why it's easier to hit with a 12 than with a .410.
[MYTH #4] Long barrels don't increase velocity. You will read that powder burns entirely in the first 18 to 19 inches of the barrel, so any additional barrel length has no effect on velocity. Untrue: Shotshell velocities don't change as dramatically as do rifle velocities as barrel length increases or decreases, but they can differ a few feet per second per inch of barrel, especially with the slow burn-rate powders used in many steel loads. Bear in mind that manufacturers typically list shot-shell velocities based on results from a 30-inch test barrel. If you're one of those who shoots a little stubby thing in the duck blind, your 21-inch-barreled gun may be shooting measurably slower than the 30-inch-barreled pumps and autos on either side of you using the same ammunition.
[MYTH #5] Magnums are fast. Many shooters believe that magnums are faster and harder hitting than standard loads. That's perfectly true if you're talking about rifle calibers; centerfire magnums are loaded to high velocity, but magnum shotshells contain heavier shot loads. As manufacturers increase the shot load, they have to decrease velocity to keep chamber pressures at safe levels. Therefore, although magnums have more shot, the individual pellets aren't getting to the target as quickly or hitting as hard as pellets from a lighter, high-velocity load. If you consistently hit birds in the back end with magnums, lighten up your loads and see what happens. Shotgunning doesn't have to be a "hit or myth" proposition.