Originally Posted by hkruss
Probably no more than 10-12 inches. I figured such a short barrel would have opened up the pattern a little more even though he was only 10 feet or so from the first wall.
Yep, and results vary widely even with nearly identical shotgun configurations, nevermind totally different shotgun setups.
I had an 870 Police once with an 18" cylinder that with Federal 00 2 3/4th typically was about 12" patterns at 15 yards. Not exactly street-sweeping patters huh.
It is not uncommon, especially with hunting style shotguns, to get a fist size pattern at 10' with anything you put in it. The old rule of thumb about 1" of spread per yard of flight is pretty accurate usually.
If you desire a wider spread up close, some things you can do in combination to get a bit wider pattern are 1. Put in the tightest choke you have 2. Load un-plated shot...as in soft lead 3. Use the kind of wad that has little or no cup.
Soft un-plated lead deforms easiest. A wad with no cup offers little protection from deforming the pellets. The tight choke helps deform the pellets. You probably already know that the more deformed the pellets the more rapidly the pattern spreads, as flat spots on the pellet sphere cause erratic flight. On the other hand...there's always a negative to every positive...to get that hard stopping performance the shotgun is renowned for, you need a fairly tight pattern and a center mass hit. Those big Hollywood wall sized spreads in reality even if you could make them they wouldn't be very effective at quickly stopping a man.
Some of the biggest and most dangerous myths are probably that you don't have to aim a shotgun and that a shotgun always absolutely instantly drops an adversary...right behind those are the famous "bad guys run away when they hear a shotgun pump get racked."