Way back when I was young and learning the slide rule the only project I could come up with that interested me was the comparison of a .177 pellet (Benjamin pump) to a .22 short. As I recall the .22 short had about 3 times the energy of the pellet. Maybe 4 times.
So the .22 has more power than the pellet. Big whoop. You only need 4 ft/lbs of impact energy to kill a cottontail dead with a .177 pellet. My .177 Beeman R-9 can deliver over 2 times that amount to the 50 yard line shooting Crosman Premier Lights with a BC of .028.
The sales people who say a pellet gun rivals a .22, well, LIE!. Maybe that ignorant, but they IS wrong. Now we have computers. Not to say the best made pellet guns are not super accurate at 25 meters tops. Then there are the pellet guns from Mexico that shoot pellets with a .22 blank for power... Listed in Gun Digest Annual in years past.
They aren't wrong. The best made pellet guns aren't .177 Benjamins, cool though they may be. The best made pellet guns suitable for hunting small game are accurate enough hit the magic spot behind the eye and below the ear of a cotton tail rabbit at 50 yards. In California, you can legally shoot upland game birds with an air rifle (subsection 311f, title 14, CCR) and the kill zone on a quail is roughly 1.5" in diameter. I didn't have any problem at all killing valley quail at distances out to 57 yards with a .177 R-9. While it is true that you do need a certain amount of energy to cleanly kill small game, that amount is actually pretty darn low. Any excess is expended in the atmosphere on pass through and the resulting impact with whatever ultimately stops the projectile.
Here in the Cookson Hills of Northeastern Oklahoma, I like to go squirrel hunting on a 550 acre patch of public hunting land on the top of what passes for a mountain around these parts. No way would I want to shoot squirrells out of the trees with my 10/22 there. The surrounding lowlands are dotted with smallholdings and without a good backstop, who knows where a .22 bullet will fall under such conditions? But I know that my pellets won't travel more than 500 yards, even if discharged at optimum angle for maximum range. The maximum range isn't high, and that is the attraction. The maximum effective range on small game, however, is a darn sight more than 25 yards, even with a little weenie middle magnum springer like an R-9. It is accurate enough for me to reliably and effectively kill squirrells, rabbits, and upland game birds (where legal) out to 50 yards and beyond. Wind plays havoc and a breeze that will barely affect the flight of a .22 LR round will drift an airgun pellet, but shoot one enough outdoors, and you get really good and "doping wind" and that isn't a bad skill to develop, because it translates over to other shooting disciplines.
That bullet mass compared to the pellet guns makes a ton of difference. Carries more energy farther. At the same time, you want to be sure of target, sure of background (anytime) and restrict yourself to head/brain shots. Lung shots will leave the animal to wander all over looking shot which drives the animal rights nuts NUTS!.
Not so fast there, Pardner...... Velocity is squared in energy calcs while mass isn't. So it isn't all about mass. It is also about a thing called ballistic coeffecient, and in my .177 R-9, the highest it gets for me .032. That's paltry, but that's okay because it is adequate to deliver a 50 yard effective range, but limits the maximum range potential to not much more than 500 yards. That lets me safely take game with an air rifle where I wouldn't want to try with any rimfire firearm. I am going to take exception to head and brain shots only, too. I heart/lung cottontails with a .20 R-9 frequently, and the result is pretty much ffffffffft / flop, every time. Ditto with gray and fox squirrels. They are much tougher to kill than cottontails, but they'll succumb to a heart/lung shot with a .20 pellet from my R-9 plenty quick enough. They don't run off bleeding all over the Northeastern Oklahoma countryside, either. They just fall out the trees and die before they hit the ground. They'd do the same if I hit them in the same spot with my 10/22, as well, but with that rifle, I have to worry about it also doing the same thing to somebody's kid a mile or two away. I don't have that problem with the air rifle.
-JP