But I still find it weird that a small .22 short, with light bullet and light load, generate higher pressure than a heavy bullet and heavy load .45 colt. I’ve shot both cartridges, and the difference regarding recoil and sound is significant.
Some aspects of this question are simple and some not. All together it's a complex question with a good many facets. A person could look at Robert Rinker's book
"Understanding Firearm Ballistics" and get the whole picture and answer.
The 22 lr. operates at max pressures of 24,000 psi
The 9mm has a standard max pressure of 35,000 psi
The 44 Spl at 15,500
The 45 Colt at 14,000
The 357 Sig at 40,000
The 454 casull at 65,000
We can see this below and it's as good a reference as others for what we want to see.
http://www.lasc.us/SAAMIMaxPressure.htm
At first look it has no rhyme or reason. But when we consider the weight/mass of the bullets involved, the amount and type of powder, and the size/diameter of the bores something begins to come into focus.
The U.S. Army uses the 22 lr for training and such and it provides some interesting figures for what it uses. I've highlighted some.
Long Rifle:
Long Rifle (Lead Bullet), propellant: 1.7 gr smokeless, bullet: 40 gr, overall length: 0.984 inch.
Long Rifle (Commercial), propellant: 2.1 gr smokeless, bullet: 40 gr, overall length: about 1 inch.
Long Rifle, M24 (Jacketed Bullet), propellant: 2.5 gr smokeless, bullet: 40.5 gr, overall length: 0.995 inch.
The first type specifies standard or target velocity .22 LR while the second is common high velocity commercial ammo. While these soft lead round nose bullet types were suitable for training or target practice, they are not legal for use in a war zone. Since .22 LR air crew survival weapons would probably be used in a war zone and could be used for defense, the M24 round is loaded with a hard lead-antimony alloy core bullet with a gilding metal jacket.[24]
The amount of powder used in the 22 lr. is at it's max with the 2.5 grains used in the M24 round. That is a tiny amount of powder compared to centerfire rounds. It's also a tiny case that is too small for a primer so it's a rimfire. So to get a 40.5 grain bullet out of a, lets say, 20 inch rifle barrel with enough energy to do it's job of killing small game, it takes a lot of pressure. Too much pressure and the thin case will rupture (long before a split barrel by the way).
Most loads in use for the 22 small, long and long rifle do not operate at max pressures but below The CCI stinger operates at pressure closer to the max then lead target rounds. Note the lesser amount of powder used for target practice by the Army.
Another point to take into consideration it that while we have bolt action rifles and revolvers for the 22 short and the (basically extinct) 22 long and 22 lr, only the latter will reliably operate most semi auto pistols, rifles and carbines.
When we use a garden hose we usually place a nozzle on it to artificially decrease the diameter of the hose (the pressure of water in the hose remains the same). This increases the speed with which water flows from the nozzle. This is similar to what happens to get a light weight 40 gr. 22 caliber bullet backed by less than 2 grs of powder out of a 20 inch barrel at 1200 fps. With the small amount of powder involved it needs increased pressure to function as it does.
With the 22 caliber 223 Remington we use a max pressure of 55,000 psi to get the same weight 40 gr. bullet to move at over 3,000 fps. For comparison the 45-70 Government operates at 28,000 psi. The latter is a much more powerful cartridge suitable for big game.
There is more involved in this of course. But with this we can look at the relationship of caliber, bullet weight, amount of powder and type, primer and see a pattern emerge in chamber pressure. There is also logic in the cartridges that began as black powder rounds and those that began as smokeless.
Hope this helps.
tipoc
