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Ultrastu

Bc testing

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The whole bc thing and how to work it out is beyond me,  I'd never even considered it until I came on here.

I didn't imagine your figures would be wrong just strange that there a lot lower than someone else's,  can a different rifle have an effect on the BC? 

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Yes absolutely. 

If a pellet really doesnt sit well inside a bore or it gets released badly at the muzzle then it will wobble and yaw all the way to the target. This will increase the drag on the skirt of the pellet and reduce velocity and hence the bc.

Thing is with a pellet ,that is stabalised by the air flow over the skirt .

The higher the inherent bc of a projectile ie .mass and slipperiness of shape the less likely it is to fly straight (im talking upto 950 fps here)and if it doesnt fly well then the bc drops .

There is a fine line between just enough skirt drag for stability and accuracy and and too lower  drag that the bc drops .

It would seem that the 8.44 grn jsbs have hit the perfect cross over point .

Between mass, bc and shape .

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Ok next round of testing .this time with fac .177 bsa pcp .at 20 yds 

Jsb exact 4.53 0.0250

Bisley magnums 0.0200

Jsb heavies   0.0385

So the bc of the  exact went up slightly from 0.0245 at sub 12 to 0.0250 not hugely significant 

The bismags dropped a lot from 0.0235 at 12 fpe to 0.0200

Which is significant .

And a different batch of jsb heavies from the 12 fpe gun went from 0.0254 to a wopping 0.0385 .which is crazy high .and means im gonna have to investigate these more thoughly through this gun .

And finally .i tested just the jsb exact8.44 at 40 yds as well as 20 yds .to see if there was any significant bc difference . = 0.0265  so up a bit next i will have to test them at 60 yds (wind free) to see if there is a trend  .

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