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Old 4th October 2013, 10:10 AM
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Brian.Samson Brian.Samson is offline
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Member of: Pontefract, Doncaster Airgun Range
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Originally Posted by rich View Post
And maybe this gives an insight into the reason why 7.9s behave differently from 8.4s even though the trajectories are much the same, at the same power. The 8.4s are strongly waisted but the 7.9s are tubbly little fellers.

In the quarter second or so that it takes a pellet to reach a 55 yard target I would be surprised if it had reached equilibrium with a crosswind. Have to take the wife out to the shops now but will do some sums on that later.
It might not be that they're stubby (although it might).. but if the trajectories are the same but the 7.9's have a higher MV - that will mean (assuming the current wind calculation is totally correct) that the 7.9's will have a tendency to be worse in the wind.

I'm only saying based on the accepted wind calc for bullets, but it's true to say that a pellet with a lower BC and higher MV will be more affected by wind than one with a higher BC and lower MV. I'm not sure of the proportional weighting for each of those parameters though.

And it could also be that Yaw Motion and the Magnus effect have a different (i.e. more significant) effect than they do for bullets. Which would explain why the wind drift calculation has been in use for so long, but why it doesn't quite work for airgun slugs.

Ok, the whole wind question has made us drift away from the original question a little bit... but I think it's been useful (I've certainly learned a lot) and I think we could potentially modify the theory a bit now.

So what we're looking for is a pellet with the highest downrange velocity, but the lowest MV (so the one with the best BC) and we're still looking for a pellet that has the least deviation in downrange velocity. I still don't know what order of importance to place on those variables though.

Oh and to carry on testing this theory out, we feel that we need to have a few chrono's set up in a wind free environment with a PCP set up to remove as much human error as possible.

Oh, something else that looks interesting is that my TX seems to come out with a pretty good BC for Exacts - better than the EV2's in Si's tests. So... that would suggest that a springer (well mine at least) is likely to take less wind than Si's EV2's (even with a JO mega air stripper fitted). Well - in theory anyway. But didn't Jon Harris say that either earlier in this thread or in one of the other pellet threads?.
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