Over the years I've thumped quite a few critters with .177s, .20 and .22 springer air rifles of various power ranges with numerous different pellet designs. Critters have ranges from small field mice, small and large rats, Columbian ground squirrels, California ground squirrels, smaller brush rabbits and jack rabitts of various sizes. One thing I can say is that regardles of FPE the .20s thump harder than the .177s and the .22s thump harder than either the .117 or the .20s. This is withpellets of equal design. Simply a matter of the cross sectional mass that hits home. The larger the diameter the larger the thump. Comparison of .177, .20 and .22 CPs out of M48/M54 RWS rifles for instance; the comparison is pretty valid as all three calibers are in the 20 FPE range. Yet visual anallysis of "kills" will plainly tell that the .20 kills better than the .177 and the .22 kills better than both of them. My guestimate based on quite a few kills is that the R9 .20 cal with CPs at 666 fps kills about as well as .117s with CPs in the 850 to 900 fps range. Over the 20 to 40 yard practical range most air rifle kills are made at I haven't found "flatness" of trajectory to be that much of benifit to the faster .177s. All of them will do quite nicely with the right pellets and proper placement of the shot. No matter how you slice it though, bigger is better.
Larry Gibson
Absolutely Larry! A .20 pellet has a 21.7% superior frontal area surface advantage over .177 and that advantage is 35% for a .22 over .177. The diamater could literally be an invisible or thin line over the broadest points of a circle. Take for example, a two bladed broadhead. That's a perfect example of diameter. Not much frontal surface on a two bladed broadhead (even a large diameter one) to be sure but still some!
The frontal area of a bullet (or pellet) is that part of the bullet (it's surface if you will) that is actually making contact with tissue. With every increment of penetration, a .22 pellet is crushing 35% MORE tissue, bone, and organ. How much does that 35% matter? If I hit a sparrow or starling flush in the breast, the .177 will kill it as cleanly as anything, including the .22. Likewise, if I put a .177 pellet through the brain of a woodchuck (even a large one), that animal may do alot of flopping around but he ain't EVER going to be any deader than the split second I squeezed that trigger! A .22 pellet won't kill that 'chuck any faster or deader. Finally, the 35% superiority of the .22 won't help me with critters that are beyond it's capabilities. A lung shot coyote,for example, is most likely to be lost with either .177 OR .22.
The advantages of the .20 and the .22 start with 1 pound animals and birds. Crows and pigeons start showing the differences of the .20 pellet, let alone .22 and .25. Needless to say small game and pests of a pound and more that CAN be taken with a good chest shot (squirrels and rabbits) are best taken with .20 and larger. I am speaking chest shots here!
Larry, I KNOW you know all this stuff. I used to enjoy your posts on the old AGLF. I just thought I'd add a few thoughts to the already excellent post you wrote! ---Mike