" RA4 "?
Hard Air speeds appear to be a comprise between 12ft-lbf and today's achievable full power (FAC).
Hard Air speeds appear to be a comprise between 12ft-lbf and today's achievable full power (FAC).
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Wind drift question
- Thread starter harrymoreland
- Start date
Centercut,
Good point!
HardAir trys to test BC at a constant muzzle energy, to make the test results comparable. That works fine for middle-of-the-road pellet weights. But it is an important disadvantage of their testing method if we're interested in very heavy or very light (for caliber) pellets....
Matthias
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It has always been my understanding that BC works in the opposite manner as this. The SLOWER the velocity the HIGHER the BC. This is because drag plays such a large role in a projecitle's BC number which is reported as an average at a variety of velocities.There is less drag at low velocities, but as the velocity increases, so does the drag. Here is a graph pulled from one of Rsterne's outstanding series to illustrate. Notice how the drag coefficient rises as the velocity increases? That means a slower velocity projectile will have less drag. Since drag plays such a large part in determining the BC of a projectile, if anything, the numbers reported in HAM are too HIGH for the .22 RDM and .25 MK2 Heavy for typically fired velocities.
Side Note: I have found the published BC numbers for the Air Arms 16 gr, JSB Heavy 18.1 gr, and JSB Monster Redesigns to be very accurate in my shooting. I have determining scope height the most challenging factor and had to manually adjust it in Chairgun until I finally found a height that matched the POI I was seeing on target. RSterne has expressed willingness and desire to put in the necessary work and find a better drag model for pellets than the GA model currently used. A more accurate drag model would make a world of difference.
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Centercut,
What drag function do you use in Strelock?
I'm under the impression that the chairgun GA function is the most appropriate for Diablo shaped pellets, but I see JSB has the G1 in its table.
What drag function do you use in Strelock?
I'm under the impression that the chairgun GA function is the most appropriate for Diablo shaped pellets, but I see JSB has the G1 in its table.
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@mmahoney. BC has a “sweet spot” where for a specific pellet it is highest (less wind drift) in a certain speed band. Higher or lower than that the BC lowers (and wind drift increases). The BCs posted by JSB seem to be fairly accurate from my testing, and for the specific pellets I mentioned the HA Mag BCs are much lower than reality. Here is one of Bob Sternes wind drift charts for pellets at 100 yards. The chart for BC would be the inverse since this shows wind drift. Most pellets have their best BC between 830 and 950 FPS, but some like the .22 RDM the band is higher due to the pellet semi acting like a slug.
https://hardairmagazine.com/ham-columns/the-external-ballistics-of-diabolo-pellets/
https://hardairmagazine.com/ham-columns/the-external-ballistics-of-diabolo-pellets/
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GA works about the same as G1 for most pellets out to 100 yards or more. For slugs, I’ve found that for longer distances over 150 yards the RA4 works better than the G1.
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Right,
As you get above 900fps you are getting into the "trans-sonic" range where results are unpredictable. Sometimes accuracy is good, sometimes terrible. You have to try it to find out.
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