"You don't shoot airborne targets with slugs, you use shot"
Only if you're a shit shot that can't lead a target (or in your case, likely using the wrong type of metal slug - you use bismuth for distance shooting, not steel or lead.)
" If you are hitting ducks with slugs at 150 yards (heck if you can hit them with SHOT at that distance), you need to drop this Slashdot gig and do some professional shooting."
The pros have been doing 200+ yard competitions for years. My last try at one was 2010 in the southern Mojave.
"The pros generally shoot at under 60 yards in competition"
Using buckshot, or buckshot in a wax slug, maybe, yes. MINIMUM safe fault distance from a metal target being engaged in an officially-constructed range, using metal slugs, is 61 yards (60 yard minimum target distance, one yard fault line allocation minimum.) My 1984 Mossberg M500 is scary accurate with a 26" barrel and just the pip on the end of the barrel, no rear dovetail. Men do distance competition all the time. We've got 12-gauge sabot rounds that are ungodly accurate 200 yards out with proper construction.
Also, with a typical Remington Express ELR shotgun shell, 1300 FPS muzzle velocity, you won't be losing any real accuracy until about the half second mark, when gravity starts making itself profoundly known to the projectile and it begins to drop like a rock. 750 feet, 250 yards maximum safe bet for better than 50% hit rate. I don't see 300 yards just yet, though. Just a tip up of the barrel to compensate, or use a longer barrel that's rifled. I've seen smooth-bore hits at ~225 before.
There's the Hornady SST rounds that get 2,000 FPS muzzle velocity with only a 6.75" drop at 200 yards. That's dead-easy to compensate for.
I've been shooting rifles and handguns of all sorts since I was 6 years old. Spring-piston dart pistols to single-pump breech-load Benjamin .22 pellet rifles (that were just as good as firing an actual .22LR) to 9mm to .40cal to AR-15 to M-16 to .308 crew-served to shotguns (20, 16, 12, and 10 gauge, and the ever-loved venerable .410 as I had a fairly rural life growing up in Texas, Tennessee, and South Carolina with an occasional Louisiana stint.)
http://firearmspedia.com/scatt... Yes, that is a sniper shotgun.
BTW, current shotgun record on a 100 yard grouping is 0.787 inch for 5 shots - zero magnification, red dot sight only. 200's a breeze, you just need to think about your ammunition, and possible crosswinds.
You do not believe, because you cannot conceive. Go spend some time on youtube. This guy nailed a slightly larger-than-human target with a 9mm at 1,000 yards. https://www.youtube.com/watch?... Here's a guy (not the one mentioned above) doing slugs 200+ with decent accuracy. https://www.youtube.com/watch?...