Fact: .22 pellets are more efficient than .177
by B.B. Pelletier
This question came from someone I nicknamed RWS 48 guy. He asked several questions that all point to some confusion about .22 caliber being more efficient than .177 in a given gun. I know I have mentioned this casually in more than one posting, but today I'd like to address it head-on. Incidentally, this phenomenon does not contradict the fact that light pellets are more efficient in spring guns, while heavy pellets are more efficient in pneumatics and gas guns. They are two separate issues.
What does efficient mean?
A pellet shot from an airgun has energy that relates to its weight and the speed at which it travels. This energy is imparted to the pellet by the airgun mechanism - regardless of what type it might be. Therefore, efficiency must mean the amount of energy the pellet is able to retain relative to the energy budget of the gun that launched it. This question is limited to one specific airgun, and is not a means of comparing one gun to another or one powerplant type to another. Since foot-pounds of muzzle energy is the common expression of the energy of a pellet, we will use it to examine this question.
I'm not going to theorize about this relationship. I'll just present some facts that illustrate my point quite clearly.
Let's begin with a spring rifle
Because many airguns are identical except for caliber, testing is easy. All you have to do is rebarrel a gun and measure the maximum energy in both calibers. I did this years ago with a Beeman R1. In .177, the rifle shot 6.9-grain (that's what they weighed at the time of the test) RWS Hobby pellets at 1,057 f.p.s., for an energy of 17.21 foot-pounds. In .22, the gun shot 12-grain Hobby pellets (once again, the actual weight at the time) at 907 f.p.s., for a muzzle energy of 21.93 foot-pounds. That's an energy increase of about 21 percent.
Notice that the velocity drops as the caliber increases. I believe that is where many people become confused. They don't bother to work out the energy levels. They just assume that faster means more powerful, and it doesn't.
Another spring rifle test
I also happened to test a Beeman Kodiak in .177 and .22 calibers. The .177 was very weak at just 18.9 foot-pounds, while the .22 got 24+. I also tested the same gun in .25, which boosted the energy up to 27 foot-pounds. In fairness, the .177 wasn't a factory barrel, but one that had been sleeved with a .177 insert, so let's not accept its energy as fact, but I doubt there would be a tremendous increase with a factory barrel, so the relationship remains.
One more springer
This one was a Whiscombe JW 75 with all four barrels (.177, .20, .22 and .25). The barrels can be changed in a few minutes, which makes this a very quick rifle to test. The best power I got was 21+ foot-pounds in .177, 24+ in .20, .28 in .22 and 31+ in .25. That's almost linear!
Now for a PCP
The easiest PCP I know of for this test would be any of the AirForce rifles. They are made to change barrels in a few minutes and are even easier to change than the Whiscombe. A Talon SS that I tested in .177 shot a 10.6-grain Beeman Kodiak pellet at 944 f.p.s. for a muzzle energy of 21 foot-pounds. It shot a 21-grain .22 Kodiak at 732 f.p.s for an energy of 24.99 foot-pounds.
Where does it end?
This energy increase does not continue forever. At some point, you reach diminishing returns and the energy starts dropping as the caliber increases. The rifles I have selected to demonstrate the relationship are all very powerful airguns. What if we were to look at other examples? As it turns out, there are two good ones.
The RWS Diana 48/52
The RWS Diana 48/52 was made for a time in .25 caliber. You could buy it in .177, .22 or .25 - your choice. Now, I don't have any test data and it would be hard to obtain, because this rifle has a pressed-in barrel that's not easy to exchange. But just from the advertised energy, we get this: .177 cal., 18.54 foot-pounds; .22 cal., 21.59; and .25 cal., 21.79 foot-pounds. The .22 and .25 are virtually the same. There will be more variation from gun to gun than between the two calibers. Apparently, this rifle peaks in .22 caliber.
This is a lightweight breakbarrel that was used several years ago by BSA as an entry-level airgun to break into the American market. It performed as follows: .177 cal., 13.9 foot-pounds; .22 cal., 15.8 foot-pounds; and .25 cal., 14.9 foot-pounds. I would guess that the compression chamber did not compress enough air for the .25-caliber pellets.
I hope these data are convincing, but if not, you can always conduct your own tests to see what you discover. I believe you will see similar results, but if not, I'd like to hear about it.