Depending if your barrel is that long -
You couldn’t hit the broad side of a barn at 2 feet with the thing!
Does the adapter have rifling in the bore?
Love the… “quality” of the machining on the outside. Looks like it would damage the chamber of the shotgun.
As to the Argentine’s I have a box about as full as yours & but so far no complete holes in the bottom.
Neat Kynoch Dummy box. (should you wish to part with it, please let me know)
My GUESS to the CAC 12 bore is a blank for dog training, (I have the same) but perhaps others from down under will have more than a guess?
I have two of these “shell Shrinker’s” . one in 12 ga. and one in 20. I have never fired one with a regular .22, just shot cartridges. The folded crimp 22 shot is difficult to extract but the CCI with the plastic capsule work just fine and they pattern surprisingly well as long as the barrel has a tight /full choke. 25ft lethal range on chipmunks, rats, small birds and bats(without damaging the inside of a barn or hangar roof). Firing a solid projectile I believe would be a big risk to the barrel. I would not bet on its ability to avoid contact with the bore. Shotgun barrels are very thin and would certainly be damaged buy a 40gr 22 LR projectile.
I doubt a .22 bullet would damage the barrel, surely that is what this was intended for. A magnum load from a 12 gauge with double OO shot can’t be much different.
I don’t think I’ll risk firing one in my Westley Richards. The 00 buck starts out clustered together and not crossing the diameter of the bore.
German barrel manufacturer Lothar Walther also offered shotshell-shaped .22 rimfire adapters at least as late as 2009.
Similar adapters existed for centerfire handgun centerfire cartridges from .25 to .45 ACP, intended for the finishing shot at wounded animals.
Adapters for .22 / 6 mm Flobert rimfire shotshell (I presume smooth bore) were offered, too.