Those necked down powder cartridges are the genius behind the 17 Winchester Supermag, so I'd say your nailgun is a prototype.....
The .17 supermag is a .27 nail gun blank, those are the big repeaters. Mine is a .22, which would be a .17 HM2. The original .17 HMR was a .22 mag.
I have three of the same Savage bolt rifles in .22 LR, .22 mag and .17 HMR. I like the .22 mag the most for overall hunting use because it's the most predictable through wind and over uncertain distances of all the rim fires I've shot. It also carries a good thump without vaporizing the edible meat the way those blazing fast "varmint" loads usually do. I haven't shot the .17 supermag yet, I suspect it will be an excellent bench gun but not really for the walk-and-shoot style of meat hunting that I like to do. .22LR also has an often overlooked advantage in that some .22LR guns can shoot the oddball loads. My grandpa always liked .22LR for trapping and pest control because the snake shot wouldn't ruin your cage traps and if you needed to keep the noise down you could shoot shorts or CBs.
Now, if you really want to talk small game hunting and that traditional American outdoorsman feel that you get when you think back to watching your grandpa skin rabbits with his stockman when you were a kid, it's hard to beat a small bore combo gun. They are a lot like traditional knives IMO in that they are a no-frills, all-purpose working tool, and were/are often treated as such by the kind of guys who also carry traditional knives. On top of that, combo/double guns (shotguns included), like traditional pocket knives, can be taken well into luxury territory without losing any of their core functionality. In fact they usually get better! A pairing of top-dollar Holland & Holland and T.A. Davison customs will shoot and skin just as many (if not more) rabbits as a Stevens and an Old Timer. Try driving a Ferrari the same way you drive your truck.
Mine is a Chiappa Double Badger .22 mag over 410. What makes this better than the old ones is that it's a true double with two triggers. You don't have to cock a single hammer twice and flip a selector, you get an instant follow up shot in case you need that 410 to finish something wounded and running. You can also choose which barrel to shoot just by pulling the correct trigger, no flipping the lever and then having to double check at the last second.