Caliber or Power
I've been watching a lot of videos where there’s a common graphic about the difference in calibers. The effectiveness of a .25 caliber round over the .22 caliber pellet as a hunting round seems to be attributed to the 50% increase in area.
I don’t really buy this. To me it seems more likely that the heavier and slower moving pellet is dumping more energy into the target because it has....more energy to dump.
I assert that if I shot a squirrel with a .22 caliber bullet/pellet weighing 30 grains and a .25 caliber bullet/pellet weighing in at 25 grains and they deliver the same energy to the target, the caliber difference will be deminimis in the “knockdown” equation.
Knockdown is more a function of energy delivered to target, how one gets there is less important
Both are true. It's not strictly the larger size of the pellet nor the energy it's carrying when it arrives at the target. The larger caliber operates on a larger area of tissue, thus has more opportunity to transfer a larger amount of energy.
With that said, I don't find "knockdown power" to be particularly useful predictor of hunting efficacy. With airguns, shot placement is vastly more important than energy delivered. Granted, making a bigger hole through the lungs or heart will more quickly stop them from doing the thing they're meant to do. I'm just saying a .25 cal at 50fpe that misses the vitals is far less effective than a .177 at 10fpe that goes through the fusebox. I've tried numerous hollowpoints and expanding pellets that propose to have tremendous knockdown power, and indeed some of them work very well...when they connect. The issue I have with them is that they rarely have adequate accuracy at distances beyond 30 yards or so to be able to hit the small kill zone of a squirrel. Meanwhile although a domed pellet does little more than icepick through the critter, I can put it into the brain and it's instant lights out.
I agree with that premise. However for it to be possible, the .177 (or the .22) will have to create a wound channel the same size as the .25. Otherwise the smaller calibers cannot produce as much tissue damage, which is a necessary condition for being able to impart the same energy to the target as the .25. So in theory that's valid but it isn't very realistic in practice.
Several reasons why:
1. It's not easy to drive a smaller caliber to the same energy level as a larger caliber because the air doesn't have as much area to push against to accelerate the projectile.
2. There is the problem of getting the smaller caliber to expand sufficiently to create the same wound channel as the larger caliber. And if we can use a .22 that mushrooms to a .25, why wouldn't we instead use a .25 that mushrooms to a .30 and be even more effective with a wound channel that is larger still?
3. We also still have the problem that pellets which expand well are rarely accurate enough for small game at longer distances. No problem if the distances are modest but that seems like a pretty significant limitation.
I skinned a gray squirrel my Dad shot with his 177, I do not recall the gun make at the moment.
Shot it must have been a quartering away shot as entry was in the back of the ribs and I found the pellet just under the skin of her throat.
If if the picture attached, you will see that there was zero expansion and near zero deformation of the pellet. Pellets were the Benjamin domes at Walmart.
The lead ear in the air gun pellets my father and I commonly get are too hard for any real expansion against a soft target. So I will have to go on the presumption that wound channel is going to outweigh power.
Power will I’ll be needed for penetration on larger game, that is larger than cotton tails which he has shot many of and are through and through shots.
Pellets do do not really deliver any hydro static shock like a powder gun bullet does, the velocity is insufficient.
Power will help get range and penetration, but wound channel and shot placement will win.