With the limited experience I have with the round, I don't think I'd attempt taking anything over about 15lbs...and with game that size I'd limit it to about 50 yards.
This round is only effective because it shoots FAST...the light bullet fizzles off fairly quick, and lacks the ability to penetrate at longer distances. It's great for vermin all around, but it just isn't quite as effective on larger game at the longer ranges.
I think 100yds is pushing the envelope for prairie dog size game...
Most factory rifles should be able to shoot close to 1" at 100yds... many can do a fair bit better, but only if there is zero wind.
Take these thoughts as you wish. I'm a die-hard rimfire shooter...but I don't even own an HM2.
I don't think there is much it's capable of that a .22lr can do as well (or better) shooting a hyper velocity round. The only real advantage would be it looks better on the paper at 100yds (accuracy). But I really don't think either are all that "effective" in the real world at those distances.
If a few bucks more per-box doesn't bother you, I'd opt for the HMR.
