An often discussed topic is what sort of caliber do I need to hunt coyotes. Or squirrels, or rabbits. There are tables that show a person's opinion but many of us disagree with at least portions of the table. Another way of comparing is to calculate the fpe of a gun and compare that. Like I have had good experience with 22 and 177 caliber pellet guns at about 18 fpe but not so good experience with lower energy in both calibers. Perfectly reasonable way to communicate.
But airguns have to deal with the fact that our power source is really high pressure air but it is at hugely lower pressures than powder burners. A rimfire can be over 24,000 psi, for instance with center fires often over 50,000 psi. To compensate more powerful airguns go up in diameter. That makes sense because the larger diameter provides more surface area for the lower pressure to push against.
But then how do you compare larger diameter potentially heavier airgun rounds to smaller diameter potentially lighter PB rounds that are moving at much higher velocity. FPE can be used but many feel it puts too much emphasis on velocity. The velocity is squared in the formula. Elmer Kieth is an old gun writer that liked large diameter handguns and felt they had much more effectiveness in hunting than the fpe would predict. He is just an example, others believe heavier slower moving projectiles can work effectively and more effectively than the fpe would indicate. John Taylor was an old african hunter and poacher who came up with the Talor Knock Out Factor. I believe Chuck Hawks came up with the killing power formula. These are alternatives to fpe which place less emphasis on velocity.
Knowing this the spreadsheet I use to look at shot curves calculates fpe for each shot but also the Taylor Knock Out Factor (TKO) and the Rifle Cartridge Killing Power (KPS). I do not think either are necessarily better than using fpe but they are alternate ways of looking at the rounds effectiveness. I calculated the following comparison:
22LR target round with 40 grain bullet going 1040 fps. Energy 96, TKO 1.31, KPS .431
35 grain 25 caliber going 950 fps. Energy 70, TKO 1.2, KPS .275
45 grain 30 caliber going 900 fps. Energy 81, TKO 1.7, KPS .41
50 grain 30 caliber going 900 fps. Energy 90, TKO 1.93, KPS .5
81 grain 35 caliber going 700 fps. Energy 88, TKO 2.8, KPS .8
As you can see, a 25 caliber airgun would have to be very powerful to challenge any of these factors for even a target round for a 22lr. But a 30 caliber gets close on energy, is higher on TKO and a little lower on KPS. Perhaps the biggest illustration of the difference in these values is for the 35 caliber. This is a pretty low velocity 35 and it is still lower in energy than a 22lr but significantly higher on both TKO and KPS. There are on line videos of the use of the Benjamin Bulldog in 35 caliber on deer and African plains game. Power was probably pretty close to this 35 caliber example. But it worked. I don't think most would body shoot any of that game with a 22 lr unless they had to. Just another way of illustrating why the other factors may make some sense.
But airguns have to deal with the fact that our power source is really high pressure air but it is at hugely lower pressures than powder burners. A rimfire can be over 24,000 psi, for instance with center fires often over 50,000 psi. To compensate more powerful airguns go up in diameter. That makes sense because the larger diameter provides more surface area for the lower pressure to push against.
But then how do you compare larger diameter potentially heavier airgun rounds to smaller diameter potentially lighter PB rounds that are moving at much higher velocity. FPE can be used but many feel it puts too much emphasis on velocity. The velocity is squared in the formula. Elmer Kieth is an old gun writer that liked large diameter handguns and felt they had much more effectiveness in hunting than the fpe would predict. He is just an example, others believe heavier slower moving projectiles can work effectively and more effectively than the fpe would indicate. John Taylor was an old african hunter and poacher who came up with the Talor Knock Out Factor. I believe Chuck Hawks came up with the killing power formula. These are alternatives to fpe which place less emphasis on velocity.
Knowing this the spreadsheet I use to look at shot curves calculates fpe for each shot but also the Taylor Knock Out Factor (TKO) and the Rifle Cartridge Killing Power (KPS). I do not think either are necessarily better than using fpe but they are alternate ways of looking at the rounds effectiveness. I calculated the following comparison:
22LR target round with 40 grain bullet going 1040 fps. Energy 96, TKO 1.31, KPS .431
35 grain 25 caliber going 950 fps. Energy 70, TKO 1.2, KPS .275
45 grain 30 caliber going 900 fps. Energy 81, TKO 1.7, KPS .41
50 grain 30 caliber going 900 fps. Energy 90, TKO 1.93, KPS .5
81 grain 35 caliber going 700 fps. Energy 88, TKO 2.8, KPS .8
As you can see, a 25 caliber airgun would have to be very powerful to challenge any of these factors for even a target round for a 22lr. But a 30 caliber gets close on energy, is higher on TKO and a little lower on KPS. Perhaps the biggest illustration of the difference in these values is for the 35 caliber. This is a pretty low velocity 35 and it is still lower in energy than a 22lr but significantly higher on both TKO and KPS. There are on line videos of the use of the Benjamin Bulldog in 35 caliber on deer and African plains game. Power was probably pretty close to this 35 caliber example. But it worked. I don't think most would body shoot any of that game with a 22 lr unless they had to. Just another way of illustrating why the other factors may make some sense.
