As a follow on from my Self Reliant Airgunning - Pellet Production post , I thought I'd show a quick method on how I've been calculating
BC without getting too technical.
The theory is pretty
straightforward. I don't have two chrono's, just a combro, so I am
relying on Chairgun and its 'BC based on POI difference' calculator.
Ten
shots in total were fired. 5 at the zero of 12 yards, 5 at 30 yards.
This gives us two distances. The fall of the shot will tell us how the
pellet is performing in the barrel, then the air as it reaches its
target. Of course, the chrono is telling us how fast it is leaving the
muzzle.
Now, this is important. The database BC was very
different from my findings. This is due to manufacturers taking an
average performance figure, in the same way they take an average pellet
weight and print it on the box. It's convenient and accurate enough for
most peoples needs. Evidently, not mine!
When I was weighing the
pellets I made, then a manufactured tin, I saw how we take so many
figures for granted with out bothering to check and measure for
ourselves. So no wonder we all have those 'mystery' shots that take us
aback. Especially when changing pellet brand.
After the shots
were fired, the average fps was taken (703.9 fps with a 10fps variation
possibly due to a strip down just prior to the test) then the groups
analysed and measured.
Accuracy
on the bull would come later, for now, a clear grouping was sufficient.
(I couldn't help but fiddle with the windage, though not elevation)
I settled for a rise of 0.896" over 18 yards. (click images to enlarge)
My
old zero was 12.1 - 27.5 yards before the strip down and the RWS
Supermags were calculated to be 0.0062 @ NTP already a big difference in
performance (or calculations!)
Here
we have the new zero and a graph that should accurately reflect the
performance of my rifle and the pellet of choice. Chairgun will then
update the pellet database for you with your BC calculation.
Yet another variable in airgunning to consider, measure and adapt to. Who said it was all 'point and shoot'?!
This is fantastic!
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