Re: 22LR vs 17HMR
I agree 100% with TP (that's Top Predator, not Toilet Paper, though I agree with using that, too).
I have them both and love them both. For a strict trainer, you are better off with a 22LR. It will give you practice doping and shooting at UKD. The 17 has very little drop. I use the same dope at 50 and 100 and 200 isn't that much of an adjustment. For the 22, I zero at 50, have 1.1 mils of come up at 100, and about 7.5 mils of come up at 200.
I had fun once shooting turtles as they popped their heads up at one of our tanks once. The shots ranged from 50 - 75 yards and if you didn't dope properly for those distances, you were guaranteed a miss. That is good practice. I would have been a lot more effective with a 17, because I would have just been able to lay the cross hairs on the critter and pull the trigger as opposed to fudging .1 or .2 mils.
The one reason to go with a 17HMR over a 22 for a trainer is that you can get a pretty dead nuts accurate 17 HMR for $350. At 100 yards, my $350 17 HMR and my $2,000 22LR are close in accuracy and at 200, my 17 HMR wins. You can get cheap 22's, but to get them to the level of accuracy I like, you have to drop some cash on them. A 17 is what it is.
I have a Marlin and and Anschutz (17HMR), and they shoot very similarly. Now I love the Anschutz more, but that is probably because I spent a lot more on it. Well, it also has a better stock and a rail and better mags and better machining.
To summarize: 22LR.