I, too, only recently learned of Lewis' "Red Ryder BB gun."
It's discussed in Carl P. Russel's "Firearms, Traps, and Tools of the Mountain Men."
Russel's research seems to disagree that you could shoot 40 balls without recharging the gun and without loss in muzzle velocity. Per Russel's account, you could fire a few rounds at the same velocity, after which power would start to decrease (which makes sense.) Russel says the air gun wasn't useful against large game, and wasn't real effective at taking down people after the first shot or two, but you could (with loss of velocity) shoot 40 consecutive rounds rapidly, and that consistently impressed the native Americans. So Russel's account is largely in agreement with the above. I agree it's really cool to see the gun and hear more detail on it. I mention it in case anyone else wants to read a bit about Capt. Lewis' air rifle.
So does this mean BB gun scenarios should be the next big wave in CAS shooting?