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Old 16th April 2015, 05:19 PM
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Tench Tench is offline
WHFTA World Champion 2016.
Join Date: Sep 2009
Location: derby
Posts: 1,423

Originally Posted by Brian.Samson View Post

The highest measured BC for a JSB 8.4 variant I've heard of is 0.027, the lowest I've personally measured is 0.018 but I have heard of 8.4's that are lower than that.

If the BSA barrel can achieve a higher BC than 0.027 with 8.4's then it will be better in the wind than any other gun on sale at the moment. Which would be a real step forward in airgunning!
Brian I have measured the velocity of 8.44 Exacts at the muzzle and down range achieving a bc of .0267 over 27y in doors using my Hornet. I have also plotted the trajectory of my Gold Star by measuring from the cross hair. I drew crosses on a box and labelled then 8, 10, 12 etc to 45 yards. I put the box at the measured distance and fired 3 shots with the crosshair placed on the cross, I did this at each distance (measured) and arrived at the following measurements for the poi from the cross hair. The scope height is 1.6" JSB exact 8.44gn @ 784 fps.
8y -11mm
10y -5mm
12y 0
13y +2mm
15y +7mm
20y +15mm
25y +21mm
30y +23mm
35y +21mm
40y +7mm
45y -5mm
Now plotting this in CG and juggling settings to make it fit requires a bc in the region of that measured with my Hornet and it still doesn't quite line up with the actual achieved poi's but this is the trajectory the rifle is shooting. It would also seem the actual optical line of sight is slightly above the measured scope centre as using 1.7" aligns the poi's better.
Doing it this way eliminated scope magnification and reticle spacing errors.
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