I have found little difference in the price between .410 gauge and 28 bore cartridges, or 16 bore for that matter...Of course far more expensive then 12 or 20 bore shells but then there are so many more of them...
I started my first batch of daughters (4) on the .410, like I was taught, my brother and sisters, uncles and aunts were taught because that's the way its been done...No recoil to speak of to scare the child, induce flinching and in a single shot, exposed hammer model, light to carry and with a visible safety (hammer) so gun handling/safety could be stressed...
The problem is that we missed, a lot and that builds frustration, which breeds dislike, which means the children didn't want to shoot anymore...luckily I had a 20 bore handy and started them on that (after learning the basics), their scores improved, frustration decreased and they wanted to come out to the range with me to go shooting...Now all are in their late 30s and all still shoot competitive clays (one was an Olympic tryout) and hunt...
My second batch of daughters (6) I started on the 28 bore SxS that I had gotten and the felt recoil is almost the same (heavier gun) which is negligible, but with about 3 times the same size pellets as the .410 hits were far more common, thusly less frustration and I then didn't have to force the girls to come out shooting...After just three days, they would be shooting as well as their older siblings when they switched to the 20 bore...
There is a reason the call the .410
The Experts Gun...in these strings posted from the Skeet championships shows:
Longest continuous string in competition
American Skeet Assoc. Records
Bore...Men....Woman
12….... 2462….... 1183
20….... 2173…..... 801
28….... 1718…..... 443
410….... 777…..... 265
Dbls…... 710…..... 259
Information Sites to specific bores/gauges
16 Gauge Society
410 Shotgun Resources
I love the 28 bore (almost, but not quite my love for the glorious 16 bore), I have SxS, O/U, single shot and semi auto guns in it...It is the perfect dove/pigeon gun, excellent for grouse/quail and more then adequate for pheasants but I still use a 20 (switching over slowly) and I've taken ducks over decoys with it...It is the ideal gun to take to Argentina et al for those dove shoots where they supply you with 3,500 shells for 4 days of shooting and they don't expect any back...My Franchi AL48D semi is so soft shooting that if it didn't go bang, you'd not know it fired...
For the added expense of a couple of dollars a box of shells against 12 bore shells, I rather shoot something softer, my 28, and not have to punish these old bones as much and it isn't as if I'm going through
dozens of boxes a weekend dove shooting, like I used to before!
For the popularity of the .410 I believe has to do more that it's been around for so long and so many people have started on it and of course there are hundreds of thousands gun already produce in that gauge whereas the 28 bore is a relative newcomer to the scene and wasn't readily available in cheap, single shot shotguns...Price of shells really wasn't an issue--both were expensive but availability and of course shot/dram selection was which of course the .410 won out on...You could into any hardware, general store out in the country and you'd find 12 and .410 and maybe some 20...back when I was a kid it was 12, 16 and 410 and hardly ever any 20s...
Today I try to hunt exclusively with the 16 and 28 bores and compete with the 12 and it's been working out fine...I'm at the point where I'd sell off all of my 20s and .410s -- except for the All Gauge sets...