Okay, I actually got out and tried this today. Structure of the mock-up included 5 layers of new denim lightly taped over everything else, all the remaining layers glued together with contact cement, and that was taped to a gallon jug filled with water and capped with a couple of inches of air in the top to allow for expansion pressure. The laminate under the denim layers included 1/4" new leather, very stiff and difficult to cut, 1/8" rubber similar to tire rubber, 1/2" of 40% expanded PVC sheet, and 1/4" dense 'technical foam.' Idea being clothing layers, skin and fat (though the leather and rubber are a lot harder than those and much more resistant to cutting with a new utility knife), ribs (the expanded PVC is quite tough but slightly porous, similar to ribs in some ways) and more tissue (dense foam).
Then the gallon jug being two more layers of plastic plus and a 6" column of water - dividing by 1.8 one gets the equivalent of 3.3" of government spec ballistic gelatin. For a backstop I used my trap which has about 15 pounds of built-up lead embedded in 5 pounds of Duct Seal, in a hardwood plywood box. It'll stop subsonic .22lr easily, with nothing going deeper than 1.25" and most stopping at 1".
One shot each with rifle and pistol, each shooting Remington Subsonics, rifle at 1040fps, pistol about 930fps. Muzzle about a foot from the target.
The pistol, delivering 76fpe, went right through the jug and the bullet was sitting sideways, not quite buried in the well-used duct seal. Front half of the bullet was swollen, not mushroomed, but sort of bulged to about 0.275" average, the back half almost intact but slightly widened.
The rifle at 96fpe also went through the jug, the bullet hitting nose-first and similarly not quite getting buried. The front half bulged in a more mushroom-like shape but still swollen more in the middle of that, not flared at the nose, to about 0.30" average diameter. As with the pistol round the rifling was still very clear on the back half.
The expanded PVC layers were shattered, out to about 0.6" with the pistol and well over 1" with the rifle impact. All other layers displayed only small punctures. Same for the bottle, just a small hole barely leaking with the pistol then a crack opening up to join the two exit holes with the rifle shot. Path through the bottle was perfectly aligned with each barrel, looked like zero deflection. Here's a GIF showing the rifle shot at 300fps:
This is the lamination sawn in half through the two wounds:
And here's the rifle round embedded in the hardened (by thousands of rounds shot into it, lots of hammering to flatten it out) Duct Seal:
Before cutting the laminated materials in half to examine the wound channels I tried a stabbing test, for comparison to a knife attack. Not on the water jug... and not with a knife, as I didn't want to injure myself. I used a very sturdy ice pick with a 0.11" diameter stainless polished blade and very long tapered point. Could not get though the whole structure. Deepest penetration was about half way into the first layer of PVC. I weigh 205lbs. Stood on a scale while applying pressure with the ice pick and watched the scale. At peak, for several seconds, I was applying 110lbs to the ice pick. So yeah, I'd not want to be trying to defend myself with a knife, at least not by stabbing with one, and an ice pick is definitely out of the question. And it seems unlikely that slashing at loose clothing with ANY knife is a very wise move. Bare skin only, and preferably nowhere near any ribs.
My conclusion? I'd compare my silly little mock-up of the tissues involved with a human torso by suggesting that it's tougher to penetrate than the real thing. Considerably tougher. Subsonic .22lr had no problem penetrating it, then going through the equivalent of 3.3" of ballistic gelatin and at least 1/4" into a medium which I've seen stop 20fpe airgun pellets at about that same depth. Knowing what my 20fpe PCP does to squirrels - pellet going in the forehead occasionally exits the lower abdomen, but if alignment is good doesn't quite come out the butt, and if a side shot always goes clear through the head and embeds into fir fence posts to about 1/2" - I wouldn't want to get hit with even the after-jug residual energy in these rounds. Those impacts were at least 15fpe to the putty. Enough to penetrate flesh to a worrisome, though hardly likely to be fatal depth.
So does this add to the pantheon of evidence suggesting .22lr's utility as a defensive round? Seems to me it does. If I were a CCW permit holder (there's only like 20 in Canada supposedly so that's unlikely for me, as I don't guard the prime minister) I'd consider subsonics out of a 4" barrel or hyper-velocity rounds out of a 2" barrel as being adequate for 'light days' when carrying a full-sized pistol was not practical. Would it be my preference? Perhaps. I like my .22lr pistol, it shoots nicely, and I can group very well with it. It feeds and ejects neatly, has only failed to fire a few times and always with this awful Remington stuff; CCI never fails in any type, and Fiocchi, Federal and other stuff I've tried just as reliable. So the dreaded rimfire unreliability doesn't seem to apply in this case at least, and shouldn't with any decently set up and maintained pistol and quality ammunition.
