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Old 12th March 2015, 03:11 PM
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RobF RobF is offline
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Originally Posted by Tench View Post
I believe there is still a lot to learn about the influence we can have on the external ballistics with the design and setup of the action in an air rifle. I recently did a test with my own rifle where I drew crosses on cards at 8 10 12 13 15 20 25,,etc,, to 45y. I then placed the cross hair on these crosses and fired 3 shots at each. I then measured the distance of the impact from the cross aim point (cross hair) then constructed a trajectory in CG to pass through all these points. with the pellet weight and velocity set at the actual measurements. I had to juggle the scope height and BC to recreate my findings, the BC figure needed to be set at 0.0350 (jsb exact 8.44gn) the scope height actually worked out very slightly higher than the physical measurement, but within what could be true bearing in mind the erector tube could affect this. CG also uses the same zero point for the end of the barrel and the LOS which could also create an error?

This gun does take less wind than many I have used, I have not measured the actual BC calculated from muzzle and down range velocities merely using it as a way of flattening the trajectory in CG.

I had a day at the range on Tuesday and did the same test with the same pellets in my Gold Star, yet again I needed to use a BC of 0.0350 to get the trajectory to match my findings. I have measured the magnification of the scope and matched this in CG. 1" measures 1 mildot at 25 yards = 9x mag.

This GS is not a production gun, it is one I have for development that does have a few different parts.

During shooting I have found my rifle still needs to come out the kill and knowing how far is what makes for a good score, when you get a rifle that takes less wind it is a whole new variable to learn rather than in instant scoring success! Of course on the right day when a wind can take some out and some can stay in it is a benefit.

I am going to stay inside edge on every shot this Saturday with the GS to see what happens.
I've been told CG needs the scope height at the end of the barrel. This can be some way off what it is at the breech.
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