Blowback physics (LONG)
This is an interesting thread, but I think some of you don't understand what the limitations are on creating blowback operated weapons.
Blowback guns are designed using Sir Isaac Newton's law of Conservation of Momentum. Stated simply, for every action, there is an equal and opposite reaction.
Thus, the bullet weighing "X" grains, moving down the barrel a "Y" feet per second translates into a slide/bolt (weighing "A" grains) moving rearward at "B" feet per second. The following math must apply: "X" times "Y" must equal "A" times "B"
Now for .22 LR, the 42 gr. bullet at 1100fps must be balance by a slide weighing 1000 grains (estimated for Ruger Mark II?) at 4.2 fps.
One can see that, as the weight goes up for the bullet (assuming bullet speed is held constant), then either the slide must get heavier, or the slide speed will start getting pretty high pretty fast. Once the slide speed gets high enough, the breach mechanism is opening up before the chamber pressure has dropped enough, and case rupture starts to occur.
The solution here, of course, is to increase the slide/bolt mass to compensate. The problem, of course, comes when the bullet gets really fast and/or really heavy. To illustrate this point, back in the 1920's, Ordnance Corps Major Julian Hatcher calculated that a blowback arm chambered for .30/06 would need a 23 POUND breachblock to function safely. That sort of makes the whole issue of portablility problematic.
So, designers seek alternative solutions to avoid the weight penalty. If they are desperate to keep the barrel fixed (and avoid locked breach solutions), then the need to retard the blowback somehow. Heavy springs work, to a point, as is the case with the Astra 600. Gas retardation works well, as the P7 has shown. Retarded blowback, like the P9S, works, at the price of breachblock complexity. Grooving the chamber works, assuming you can control the ductility of the brass carefully. (This has proven to be a problem for military arms that use ammo from all kinds of sources.)
The key here is that WEIGHT becomes the driving limit as to why blowback is not used in many arms with power levels higher than 9x18 Makarov.
PS>>>using subguns as a comparison as to why blowback works for larger cartridges like 9x19 and .45ACP is not very valid. Most subguns weigh in excess of 7 pounds, which is far greater than any true handgun, which almost always weighs less than 3 pounds.
