Well, this cost me a whole day playing with my spreadsheet.... *LOL*.... I spent some time with ChairGun and figured out how the math works for their Penetration calculator.... I then worked out the velocity required to penetrate various distances with a bunch of pellet weights in different calibers.... and graphed the results.... The only factors taken into account by ChairGun are the Velocity and the Sectional Density.... They don't take into account the shape or construction of the bullet.... but if you use the data for comparison purposes (eg. assume a round nosed pellet).... it should provide a decent way to compare calibers.... In simple terms, for a given velocity, a .22 cal takes a 50% heavier pellet to get equal penetration, and a .25 cal takes twice as heavy a pellet, when compared to a .177.... Here are the results.... USE THE VELOCITY ON IMPACT....
The "non-PAL" graph shows the penetration at 450 fps, which I used for the velocity at 20 yards.... It uses an 8 gr. pellet in .177, a 12 gr. in .22, a 17 gr. in .25, and roundballs (44 gr. & 68 gr.) in .30 and .35 cal respectively.... I chose those weights because they are (except in .177) the lightest lead "pellet" available, which should mean the gun would be legal if tested.... Note that the three common calibers all have nearly identical penetration at about 1.75".... I didn't expect that, but there it is....
I haven't assigned likely animal/bird candidates to the various Penetration numbers, as that is so much personal choice.... However, you could do things like say 1.5" is good for mice and sparrows, 3" for crows and rabbits, 5" for Marmots and Racoons, and 8" for Coyotes.... It really is up to the shooter, but I think the relationships between calibers are much easier to understand by using these charts.... For example, to have equal penetration at the same velocity, a .25 cal will require twice the FPE of a .177....
The last set of graphs use the same method, but on big-bores.... I think from what I have read about deer hunting with air rifles, they are actually pretty darn close to what people feel is sufficient for the job.... I would use the 16" chart for deer, and possibly the 12" one for hogs.... but again, that's a very subjective thing.... Moltogordo might want to look at the last chart (24") and give it some thought as he's considering going after a bear with an air rifle....
I'm sure I'll catch some flack over this.... but I don't really care.... I'm just trying to give people another tool to consider when they are wondering what makes sense for different size animals.... and how different calibers compare in terms of penetration.... Your comments are welcome, of course....
Bob
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