Backyard BC for .22 cal

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nvelkhunter

Member
Aug 13, 2015
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Nevada, United States
Shoot Crossman 14.3 and JSB 18.13 at 0 yards and 57 yards through chrono. Base on velocity measurements and using a Form Factor of G1, Crossman had a BC of 0.023 and JSB 0.044.

Form Factor G1 is not a good match to a pellet, but don't know what to use instead that would be more accurate, so recommend not focusing on the absolute BC value. Biggest take away is the difference between Crossman's and JSB's. A lot more than I expected.
 
Actually, I provided the ballistic math for that AoA BC calculator. It's pretty simple, being based on a constant drag-coefficient model in which the drag force acting on the pellet is proportional to velocity squared...

BC = (Yards_near - Yards_far) / 8000 / LN(V_near/V_far)

Despite its simplicity, trajectory calculations based on it have been proven accurate in actual shooting to 100s of yards.
 
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A fair question. Math-magically speaking, the scaling constant of 8000 * BC is the downrange distance in yards where, if the pellet continued being decelerated by air drag at the same rate (i.e., in ft/sec^2) it experiences at muzzle velocity, and if it didn't hit anything solid, it would come to a complete stop.

In reality, because the rate of deceleration is modeled as proportional to the square of speed, the rate of deceleration decreases as the pellet slows, and the hypothetical 8000*BCyds is actually the distance where V = MV / e where "e" = the Naperian base 2.71828...

The full expression for downrange retained velocity is: V@x_yards = MV / exp[x / (BC * 8000)].
 
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