Am I calculating BC correctly?

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mubhaur

mubhaur

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Nov 8, 2015
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Karachi, Pakistan
I set the fps of my regulated .22 pcp at 940. I zeroed it at 22 yards. Then I went to 65 yards and shot a few pellets. The drop was 2.8". My scope hight is 1.78". When I put all this data either in Chairgun or Strelok, in order to bring the figure of dropped to 2.8", I have to put the BC value of 0.07. This is unbelievable for me.

Then I set my fps to 870. Zeroed it at 22 yards and shot a group at 65 yards. Now the drop was 3.3". This translates into a BC value of greater than 0.09. It's again unbelievable.

Am I doing something wrong? Please advise.

I am using JSB 18.13 grain pellets in all these tests.

Regards,

Umair Bhaur
 
I could be wrong but I'll take a swing at this. You are shooting while the pellet is rising above the line of sight. I am not sure that the developer has taken this into consideration. I would set my zero to whatever chairgun gave me for my single zero setup and then measure the drop from that point to whatever distance down range you might want. If you do it that way you can be sure that you are considering ALL the drop between the two points because the pellet is already below or at line of sight when you start to measure drop.
 
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The bc defaults in when you pick the pellet. Jsb 18 gr domes have a bc of 0.033 according to ChairGun. You trajectory seems right, why try to calculate the bc when it's a default value from the data base?

like the other gentleman said, your 22 yard zero is on the way up not down, the program is geared to the far zero. Put 45 or 50 in the far zero and check the graph
 
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