HW100 SK.22 + NSA 20.2gr -- half the BC ? 0.0277 ?

[bambuino]

Classify me as "slug curious." 

Pushing NSA 20.2gr 0.217 DB-HPs at about 710FPS from an HW100 SK .22, 41cm bbl, I attempted to calculate a BC from drops at range. Came up with a BC 0.0277, and that is about half the published 0.075. From a 26 YD ZERO, get about 1MIL (1.6 inches drop, avg 0.45" CTC) drop at 40YD, and 2 MIL (3.57 inches) at 50YD. Plugged into software for tables, returned later with good (predicted) dope at other ranges.

On background, have settled with any flavor 15.89gr diabolo for this rifle as they shoot so predictably well. Am not looking to slug tune the rifle, this is more out of curiosity.

Is my experience in this exercise a familiar one to other folks? TIA.

 

[Motorhead]

Somethings fubar ??? I get very close to the rated BC

 

[bambuino]

Thanks Scott. I will run the far chrono and see if this resolves. Am using ChairGun 4.3.8 for making tables and BC tools. Would u/l the cfg file but don't wanna risk breaking the AGN.

 

[bambuino]

Gathered some FAR chrono readings for the NSA 20.2s and an 710FPS MV. Sanity checked the Air Arms 15.9 I typically use. For the 15.9s been using a BC(G1) of 0.0351, from an 845FPS MV.

NSA 20.2gr HPs

@25YD - 674FPS / ES 10 / SD 3.22 / BC(G1) 0.0567

@40YD - 655 / 7 / 2.40 / 0.0584

AA 15.9s

@25YD - 776 / 10 / 3.37 / 0.0370

@35YD - 751 / 10 / 3.46 / 0.0371

@40YD - 732 / 17 / 6.34 / 0.0344

So, the BC of the NSA 20.2s from NEAR/FAR chronos is about 0.057, and much closer to the published 0.075. But, the dope out there still wants to give me a BC from drops of 0.0280. Practically, I have to go with that. Still though...odd.