Learned something interesting about these .20/18.9grain slugs in the last few days....
I mapped out actual trajectory from 20-100 in 5 yard increments with them going 865-870 and then compared what I had to Strelok. It needed a BC of 0.07 to line up.
I then mapped out actual trajectory from 30-100 (but only in 10 yard increments here) with them going 910-915. Comparing that trajectory arc to Strelok required a BC of 0.09 for actual to match predicted.
I've mostly shot them closer to 870-880 prior to this, always using a BC of 0.09. It appears that right around 865-870 there's exists a node of sorts where the BC isn't as high as when they're going faster.
A friend also shooting them is seeing a BC of 0.1, although it seems he's mostly shot them a bit higher yet, 920-930, if I follow him accurately.
Now, I understand that a the ballisticians amongst us will say that a BC shouldn't change with speed. But sorry, in the real world it does. And yes, that means the reference drag law isn't ideal for the projectile, but we work with with we've got.
The difference in speed (and therefore BC in this case) is that at 100 yards they need 2.6 mils of elevation with the 865-870. And they need 1.8mils of elevation at 910-915. Same scope zero of about 65 yards for both.
I mapped out actual trajectory from 20-100 in 5 yard increments with them going 865-870 and then compared what I had to Strelok. It needed a BC of 0.07 to line up.
I then mapped out actual trajectory from 30-100 (but only in 10 yard increments here) with them going 910-915. Comparing that trajectory arc to Strelok required a BC of 0.09 for actual to match predicted.
I've mostly shot them closer to 870-880 prior to this, always using a BC of 0.09. It appears that right around 865-870 there's exists a node of sorts where the BC isn't as high as when they're going faster.
A friend also shooting them is seeing a BC of 0.1, although it seems he's mostly shot them a bit higher yet, 920-930, if I follow him accurately.
Now, I understand that a the ballisticians amongst us will say that a BC shouldn't change with speed. But sorry, in the real world it does. And yes, that means the reference drag law isn't ideal for the projectile, but we work with with we've got.
The difference in speed (and therefore BC in this case) is that at 100 yards they need 2.6 mils of elevation with the 865-870. And they need 1.8mils of elevation at 910-915. Same scope zero of about 65 yards for both.
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