Understanding .410 Shotgun Shell Length: Why 2 1/2 Inches?

Question
Paul - Why is it that 'regular' .410 shotgun shells are only 2 1/2" in length rather than 2 3/4" like 12 or 20 gauge?  The .410 magnums are 3" so it seems like 2 3/4" would be plausible. I would think with a small bore you'd want to get as much lead in the air as possible. MSS

Answer
Because when it was designed all 8ga 10g 12ga, 16ga, 20ga
24ga, 26ga, 28ga, 30ga, 32ga etc a were 2 inch or 2 1/2 inch.,
When the 2 3/4 was introduced at the turn of the century
it did add more shot. It added wadding space.
Also it kept new smokeless powder rounds from being loaded
in to a black powder only gun.

Here look at the here 12 ga wads
http://shop2.mailordercentral.com/bpicart/products.asp?dept=86
now look at .410 wad
http://www.midwayusa.com/ebrowse.exe/browse?TabID=1&Categoryid=17742&categorystr...
Its basically just a shot cup.
Going from 2.5 to 2.75 would not add shot.

If your interesred
.410 bore wgen expressed as gauge 67 gauge.