Hey all - completely new here, and admittedly haven't lurked all that much (so I hope I'm not speaking out of turn), but...
I watched a youtube clip about butchering chickens not all that long ago, and there was a nice humane action that the "host" took when he off'd one of his flock.
He took a narrow knife, and slid it into the chicken's mouth in such a way that it cleaved the bird's brain in half. I hadn't heard of this before, and it appears to be a really quick, painless action to take in order to show some mercy to the bird.
If the amish don't want your roosters, this may be a much easier way to do it rather than the .22. Shooting them just seems like way more trouble than it's worth, and fraught with potential issues.
Here's the youtube "link" in case you're interested:
youtube[dot]com/watch?=vy_vutu5qO0
He explains it early in the video, and then demonstrates it at about 3:55.
Hope it helps.
Tim.