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rsterne · Moderator

Here is a question for you.... Given one pellet, the .22 cal JSB Exact Heavy 18.1 gr. fired at various velocities.... which muzzle velocity will have the least wind deflection at 25 yards.... using a 10 mph crosswind?....

This poll will run for 7 days.... after which I will give the results for each velocity.... Wink

Bob

fritz · Silver Status Member

IIRC from your previous works, they have the highest BC with a MV of about 950fps. After that it drops off again.

So having the highest starting BC should reduce wind drift.

Bozo · Veteran Member

I'm going with wind drift working like gravity. The reason slow pellets drop more than fast pellets is that over a given distance gravity has a longer time to pull the pellet down. Wind drift should work the same way; over a given distance the wind has a longer time to push the pellet sideways; therefore a faster pellet should be affected less.

yourdaddyjoe · Supporting Member

your kidding... I'm still trying to figure out when the train comes in from Cincinnati....

sniper · Silver Status Member

899 imo. from what i know that
is the optimum for that weight.
a pellet is not shaped like a bullet.

rsterne · Moderator

OK so I was busy yesterday and didn't publish the results.... Embarassed

I tested the .22 cal 18.1 gr. JSB Exact Heavy from a regulated PCP that was hooked up to a SCUBA tank where the pressure was about 500 psi above the regulator setpoint of 1900 psi.... I varied the hammer spring preload using the RVA a turn at a time.... which changed the muzzle velocity.... I shot 5 shots over the Chrony at the muzzle, then moved the Chrony to 25 yards and repeated.... for each RVA setting.... Using Chairgun Pro I then calculated the Ballistics Coefficient over 25 yards for each velocity.... Lastly, using that BC and muzzle velocity, I used ChairGun to find the Wind Drift.... for a 10 mph wind at 90 degrees to the bullet path.... Remember, that wind drift is not proportional to flight time.... it is proportional to the DIFFERENCE in flight time between the real world and in a vacuum.... Here are the results:

Muzzle Velocity; 25 yard Velocity; Ballistics Coefficient; Wind Drift @ 25 yards

1004 fps; 872 fps; 0.022; 0.98"
967 fps; 860 fps; 0.027; 0.82"
899 fps; 815 fps; 0.032; 0.74"
819 fps; 754 fps; 0.038; 0.68"
710 fps; 652 fps; 0.036; 0.81"
566 fps; 510 fps; 0.030; 1.26"

As you can see, the Ballistics Coefficient (measured over 25 yards) peaks somewhere between 750 and 850 fps.... It would take a lot more testing (closer increments) over a shorter range (5 or 10 yards) to determine the exact velocity where it peaks.... but that doesn't matter anyway as we are interested in how the pellet performs over longer ranges.... One thing to remember is that as the pellet travels downrange, the BC changes.... I'll give you an example using the 899 fps muzzle velocity:

MV = 899 fps.... 25 yd. V = 815 fps.... BC over that 25 yards = 0.032
25 yd. V = 815 fps.... 50 yd. V = 751 fps.... BC over that 25 yards = 0.038
50 yd. V = 751 fps.... 75 yd. V ~ 690 fps.... BC over that 25 yards ~ 0.037 (est.)
75 yd. V ~ 690 fps.... 100 yd. V ~ 631 fps.... BC over that 25 yards ~ 0.035 (est.)

The resulting velocity at 100 yards if we used an MV of 899 fps and a BC of 0.035 would be 628 fps.... so we could call that the "average BC" over 100 yards starting at 900 fps.... You will note that the pellet spends a lot of its flight time over 100 yards in the "sweet spot" of the BC if you fire it at ~900 fps.... Mr. Green

So the answer to my poll question is.... of the choices given.... 819 fps MV produces the least wind drift over 25 yards.... using the .22 cal 18.1 gr. JSB Exact Heavy pellet....

In the real world.... ~900 fps would be a better choice over 100 yards with this pellet.... I hope you have found this thread interesting.... If you have any questions, I will do my best to answer them....

Bob

sniper · Silver Status Member

damn professor!!! you did it again!! Shocked

i'm thinking then that the 795 fps average with my marauder
throwing kodiaks leaves little to improve on Idea

you said in a another thread that i'm still doing 14fpe@100yards.
Shocked

rsterne · Moderator

You'd have to run the experiment using Kodiaks to be sure.... and then the answer willl depend on what range you are shooting at.... but for 25 yards, you are probably correct....

Bob