? different B.C.s of the Beeman Kodiak pellet
I thought I read this somewhere. But am suffering a case of CRS. Lets use the Beeman Kodiak as an example. In what caliber is the B.C. the best? .177/.20/.22/.25? http://www.straightshooters.com/documents/pelletcomparison.html
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Got it. Been looking for an excuse to by another chrony.
5.5,
If I remember correctly, ChairGun gives two ways to calculate BC’s. IMO, the “best” way is to use two chronographs, one at the muzzle and one down range at a measured distance. The two velocities are fed into the BC calculator along with atmospherics (temp., pressure, humidity and altitude). A BC for those conditions, that pellet and rifle come out.
If you only have ONE chrony the same can be calculated by using muzzle velocity and drop over a known distance.
Hope this helps.
Abe
If BC changes from one gun to another how can calculate BC for a specific pellet in my airguns? Will measuring/calculating for each gun and pellet combination provide more accurate data…
Got good news…and bad.
The higher the number, the better.
BUT, pellets have only the potential for a certain BC. What they really get can change from rifle to rifle for various reasons (which would be a whole ‘nuter very long post).
Can look at the test results for various guns here:
http://www.straightshooters.com/navagationpages/ourtakselections.html
they calculate the BC from actual firings. Can look at different rifles, shooting the same pellets, and find that the BC of the pellet is NOT the same. Can be quite a difference.
I just looked up 5 rifles at random on that site, keeping track of kodiaks in .177 and .22. the Kodiak BC’s in .177 ran from .017 to .026 while the .22’s ran from .023 – .036. Probably a great variaion that than, I just took a quick 5-rifle sample.
So in short, think of published BC’s as the upper possibility…you might not get that in real life due to the way your rifle decides to shoot them.
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Here are two things that can reduce the BC of a given pellet (precession and nutation).
http://www.arld1.com/nutation.html
I am no expert on this kind of physics. However, this is what Wiki has to say about Ballistic Coefficient.
Shadow, the lower the number the better. Correct?
These are from the ChairGun software:
Beeman Kodiak:
.177 — 0.0230
.20 — 0.0250
.22 — 0.0360
.25 — 0.0370
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2nd best would be to get a very accurate average for 10 shots at one range…then another average to 10 shots at a longer range (can suggest 10 yards and 40yards).
With two chronographs, will still need to shoot 10 shots. Will find odd things if you calculate each individual shot. Thinks like a BC of .022….,031…..024…..025….,033….etc. then you’ll average the BC’s from all the recorded shots.
This would make it a lot easier:
http://www.airgunexpo.com/calc/calc_bcc.cfm?
If you can do accurate groups. vel. radings, and drop measurement, can kind of back-into the BC by knowing the drop over two differnt ranges range to the fraction of an inch. Don’t think it’s better this way, but it gives a pretty good ball park estimate. Need to know the scope height over the bore exactly.
Below is a set done for a Sumatra. Nube3rs are the srop below POA at the two yardages, and the average vel. Figured the BC out to be very close to .03 for that pellet, and using that for drop charts has prooven to be on the money.