Range Report Tweaking JBM inputs...where do I start?

[DIBBS]

I developed a new load for my 6x47 Lapua, using a Nosler 105gr CC. I shot two strings over an Oehler chronograph, one 10 shot, and the other 5 shot, to determine my muzzle velocity. I input the numbers into JBM, and printed out a dope card.

My come-ups are less than they need to be(a couple tenths of a mil @ 400, and more at longer range. I've attempted tweaking my inputs into JBM to match what my real adjustments were in the field. However,I haven't been successful, and I'm not sure what BC the program is using for the boolitz, (but am guessing that its too high).

I believe my velocity and other inputs are correct, but to get scope adjustments that are close, I have to lower my velocity by about 60 FPS. Since my trajectory card goes from 0-1350 yards, I could't figure out an easy way to interpolate or adjust my base data. What's my next step?

 

[BryanLitz]

Re: Tweaking JBM inputs...where do I start?

If you're off at 400, I would be most suspicous of your scope adjustment. Are you really getting what you're dialing?

BC error shows up at greater ranges than 400.

To check scope adjustment, shoot at 100 yards. 1 group with your 100 yard zero, then dial up 10 MILS and shoot another group. Measure the distance between the groups to be sure you're getting what you're supposed to. Be mindful of the exact range (100 yards or meters), it matters in this calculation.

Good luck,
-Bryan

 

[DIBBS]

Re: Tweaking JBM inputs...where do I start?

Thanks Brian, I'll double check the scope (NF NXS) . I checked and the program is using G1 (.517) for the Nosler 105 CC for the calculations. I don't have that bullet shown in the first version of Applied Ballistics.