All-or-nothing loads in .410, why is that?

[SoupOrMan]

While strolling past the ammunition locker at the local K-Mart, I noticed that .410 shotgun ammunition has an all-or-nothing philosophy: large pieces of lead like a slug or #000 buck or tiny pellets like #6 to #9 bird. The largest pellet size I've seen at all other than #000 has been #4 for bird and small game. Do shot sizes between #4 bird and #000 not fill the cartridge properly? Is there not enough space to put a decent charge of powder and say, a useful load of BB? The .410 isn't exactly an easy gun to use because of its low shot capacity, but I'm just surprised at the huge gap between #4 bird and #000 buck.

[Whirlibird]

Most of what gets shot at, and occasionaly hit with a .410 is doves, rabbits, squirrrels and other small game animals. #4 shot is large for many of these critters so the smaller shot is what's used, plus you get more of the smaller pellets in the tiny hull. Hits are what count and with half as many pellets your shot pattern becomes more luck than anything else.

The opposite end of the spectrum, the slug and 000 buck are nominally used in "defensive" purposes or for other critters. The slugs will take a coyote but won't do well on deer.

With multiple hits you get more "shock" to the system and often that's what is the effective part of using a scattergun. Look at the .22lr and .38Spl shotshells for a handgun for an example.
The .22 with it's ''dust" shot will really do a number on a rattler while the larger #9 shot of the .38 normally needs an extra shot or two to finish the snake off. The "dust" gets inside but it also overwhelmes the snakes nervous system. The desparity of shot amount notwithstanding the .22 and .22 mag are most often more useful for Mr. No-Legs.
Anymore I load my .38 and .44 shot capsules with "dust" shot and it will just decimate a snake.

[mousegun]

S&B makes a 5 pellet OO Buck load in 3" shell as that pellet size fits well in their shot cup. In the Bear brands, they have a 5 pellet #4 buck load (I have yet to get one to disect) so I must assume that they have a sabot style shot cup of some kind to make up the size difference. Those exceptions aside, here is what you end up with left:

Loading using card wads.
T shot will stack side by side (layers of two) and you can get maybe 20 in a 3" shell. BB will stack in layers of three and you can get 30-33 in your shell. #2 will get loose layers of 4 but due to all of the layers is really time consuming to load.

Loading using standard wads.
BB loads like T shot when loaded over a card wad(layers of two).
#2 is more like BB but is a PIA at the bottom due to the taper so it ends up stacking irregularly.

[SoupOrMan]

I figure if I loaded my own, it might behoove me to try out smaller shot than 00 or 000, since my old .410 is set up for 2 1/2" shells. I was thinking maybe BB or BBB instead or some mix of #1 buck and some kind of "filler" shot.

[chrisb]

The reason I think it is limited more than anything, is that the .410 is not used all that much compared to the 12 and 20.