Okay, I just want to add my 2 cents, as a newbie - been shooting IHMSA since January.
I started off shooting .44 BB, .38 FP, and .22LR SB, all revolvers, cause that's the way Major taught me

.
Since then, I have acquired an old TC Contender in .22LR, which I have used on both SB and FP at the ranges in Cochise and Tucson.
I would have to say that .22LR has been the cheapest, most versatile, and most pleasant to shoot as a newbie. I'm still chasing the turkeys on the BB course with my .44, of course, but for sheer shooting enjoyment, with no fuss or muss, and it draws me back again and again - it's the 22lr. My wife may even break down and shoot IHMSA with a .22; my dad with MD can still shoot .22 - it's an every man's cartridge.
It seems to me that air pistol has caught on real well, while "traditional" silhouette hasn't grown as rapidaly. Maybe if we hyped up the .22lr, we'd see more folks come out who are otherwise intimidated by things like recoil and reloading.
I think it'd be great to see the IHMSA become a marksmanship development game in addition to its traditional marksmanship competition. Personally, when I get comfortable and consistent shooting the .22, I may branch out and get that 7mm TCU, but I'm going to wait a bit first.