Yep, Ive had some experience the the Mach II and my son has had even more experience than I have. Hes been pillaging the local rabbit and squirrel populations with mine. If there has been a better rifle for that purpose ever built, I dont know what it is. Head shots are a given. Headless. Body shots, behind the shoulder, are reminicient of a 17Rem on a coyote. Small entrance, liquified chest cavity and no exit. Gut shots are messy. Shoulder shots ruin one leg and liquify the chest caivity but normally dont hurt the off shoulder. All these seem to be pretty predictable. Im very impressed and more than pleased. This kind of performance and you can do it accurately out to 150 yrds without having to guesstimate the distance. Impressive.
Having said that, seeing what it does to body shots and shoulder shots on rabbits and squirrels, its not going to be worth a fllip for anything bigger. It most likely wont be a coon or possum gun. Sure not a fox or coyote gun. Which, btw, you HMR is in no way a coyote gun, regarless of what ammo you use. Its nothing more than a sooped up Mach II runnin the same bullet 400 fps faster. Its a fox gun at best. You shoot many coyotes and you will cripple more than you kill. And the 20gr bullet doesnt help. It will bore a little hole all the way thru and leave very little internal damage. No free lunch, you cant have it both ways and the HMR wont do it. The frangible bullets are too frangible and the hard nosed bullets slip right thru.
Whoever said they have a 223 that splashed on a coon, please post what type of ammo that is. That makes me curious. Not saying it didnt happen, just very curious.
All in all, I think the Mach II is probably the best rimfire invented since the 22lr. Fantastic, as long as you know its limitations. The HMR on the other hand, kinda missed the niche. Too much for small game and too little for big game. I have a coon huntin buddy that tried his and was very disappointed. Wont penetrate a coon skull and tears the hell out of body shots, splashing without killing. Bad deal. I dont know that the HMR has a niche.
BTW, mine is a Marlin 717M2, Semi Auto. Great little gun.