Differences with JSB 25.39 .25 vs. 25.39 .22 in an Airforce airgun

h2okenny · Sep 5, 2019

I'm curious, I have an Airforce airgun with both a 12" .22 and a 12" .25 barrel.Today I was gathering some data on shot strings and thought I would try the 25.39's in both calibers. First I shot the .25. It averaged 825 fps over 50 shots with a 3000 psi fill. Changed out the barrel to the .22 without changing any settings and it averaged 809 fps with fewer shots. As far as difference in shot count, that could easily be me not being careful when refilling the tank, but I would have supposed they would have been very similar speeds, or maybe the .22 would have been slightly faster. Is there a reason why a .25 would shoot faster than a .22 with the same weight pellet?

JCD · Sep 5, 2019

The heavy .22's most likely fit tighter in your barrel. The light 25's have thin skirts.

nervoustrig · Sep 5, 2019

The larger caliber has more area for the air pressure to push against, thus for a given air pressure, there is more force accelerating the larger pellet.

h2okenny · Sep 5, 2019

Makes sense I guess. With my redneck logic I figured since I was using the same amount of air within a smaller bore that the .22 would have been marginally faster. Then I thought, maybe the .22 pellet is longer and would have more drag going down the barrel which could contribute to it being slower. Then I thought, why not ask some folks who might actually know what they're talking about.

nervoustrig · Sep 5, 2019

Drag is not the reason. They are both diabolo shapes so there isn't a lot of contact with the bore. There's just a small band of contact at the head and another at the skirt. If one were a solid cylindrical bullet and the other were a pellet, the difference in drag could very well be significant.

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Differences with JSB 25.39 .25 vs. 25.39 .22 in an Airforce airgun

h2okenny

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JCD

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nervoustrig

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h2okenny

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nervoustrig

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