That's what my cousin says. I'd go 00 as well. Not that 000 wouldn't do fine as well...
Sure it's going to be on sale but how many will you use in your HD scenarios, hopefully none! Instead of buying price buy quality or in this case quantity!
The F.B.I. uses #2 buck, many SWAT/HRT teams use either #2 or #4 and I've experimented with so many combinations that it near drove me nuts...My favourite commercial load is a heavy/magnum loading of #4 buck.
I found the ideal load was #BB (.180/46.5 oz) as a filler for #F (.220/28.1 oz) buck. Another that I found very effective was a load of #2 bird as filler for a load of #2 buck but then I handload so I can make up anything I want.
Since your ranges are going to be within, maximum, 15 yards, unless you live in a huge mansion, then it doesn't matter what you practice with as long as it has the same velocity so you can get used to the recoil and there you can get whatever you want from #7½ to #BB for what ever is on sale after duck/goose season will be the best as you'll need magnum loads to compete against even reduced loads of buck.
The problem with birdshot, especially below #2 is their inability to go through heavy clothing because the individual pellet just doesn't have enough mass to do it where the bigger and heavier pellets will. It is mass and velocity that cause penetrat
ion, take away one and the other won't do it (or won't do it as well)!
A standard 1 ounce load of #9 is 585 pellets, #4 is 135, #4 buck is 24 and #00 is 8 and that’s just to make an ounce. How much does a single pellet weigh.
The object of a shotgun is to put a spread of shot into an area that the target will fly into. It is not an aimed firearm--so to speak but a pointed one. The more pellets in the pattern the less chance the target has of getting away unscathed. A 12 ounce upland birds doesn’t require many pellets to down it; nor very big ones at that. The unfortunate fact is that the bigger the game animal the bigger the pellet required but with far less pellets in the shell.
A Magnum load of powder takes some of the room away from a load of shot and that’s why the made the 3” and then the 3½” shotshell—to get more powder (higher velocity) and more pellets (mass) together to get the job done.
I have a 3” and a 3½” coach gun that I have rigged for a HD (Home Defense) gun but I won’t practice with the 3½” shells. I went and bought two 5 packs of them, fired one out of each barrel—to see where and how they patterned and put the rest of the shells in the stock sleeve. Did the same with the 3” shells and for practice with both I use very heavy loads of 2¾” shells because they are so much cheaper to buy or load for.