BC question

[hogpatrol]

I am using the AP program to create drop charts. Am shooting a 26 Nosler, 130HVLD @ 3465, 1-8.5 twist, 50msl, temps in the 30s. Referencing to the program's trajectory chart, POI is one minute high at 500 and 1 1/2 minute high at 800. Should I change the velocity or the BC to get it to match up? So far accuracy hasn't been to bad. Shot at 800 with a variable left to right wind. Aiming point was ballpark in the middle of a 18" plate.

 

[Bryan Litz Ballistics]

Before you go changing MV or BC, it's important to make sure your 100 yard zero is solid, and that your scope is tracking true. In other words; when you dial 10 MOA, are you getting 10 MOA or 9 MOA? This error is common and it often makes it look like ballistics programs are off when they're not.

After verifying your zero and scope adjustment, if your trajectory is still off, you should calibrate your MV. This is best done at the furthest supersonic range you can get a good target (range where your bullet stays above about 1340 fps).

AB Mobile has a ballistic calibration feature that will calculate your MV automatically based off your range and observed drop. You access this from the solution (HUD or drop chart) screens thru the menu > ballistic calibration. Tell the computer how much drop you saw at the range you're shooting and it will calculate the correct MV.

Hope this gets you on,
-Bryan

 

[Berger.Fan222]

Before you go changing MV or BC, it's important to make sure your 100 yard zero is solid, and that your scope is tracking true. In other words; when you dial 10 MOA, are you getting 10 MOA or 9 MOA? This error is common and it often makes it look like ballistics programs are off when they're not.

After verifying your zero and scope adjustment, if your trajectory is still off, you should calibrate your MV. This is best done at the furthest supersonic range you can get a good target (range where your bullet stays above about 1340 fps).

AB Mobile has a ballistic calibration feature that will calculate your MV automatically based off your range and observed drop. You access this from the solution (HUD or drop chart) screens thru the menu > ballistic calibration. Tell the computer how much drop you saw at the range you're shooting and it will calculate the correct MV.

Hope this gets you on,
-Bryan

Good advice. Before adjusting your muzzle velocity to match your trajectory, there is also benefit in double checking scope height above the bore and actually measuring the local pressure, temperature, and humidity.

 

[hogpatrol]

Thanks for those possible errors. I used the GPS data and actual local atmospheric conditions from the phone in the AB program. Also using a Nightforce 5.5-22x56 NXS, nothing guaranteed but that scope should be true. Entered the azimuth, scope height is correct. 100 yd. zero is 1" high. I did chrono it with a magnetospeed when the temps were in the teens (RL33 powder) so that may be a factor although I wouldn't think 25 degrees on the warmer side would be that much of difference unless ambient temps were very warm. Action & barrel haven't been removed, re-tightened or otherwise disturbed since the chrono session. Entered the azimuth, scope height is correct, 1.8.
Having said all that, I'm going to go back and double check all rifle fixed data, and shoot some targets at 300 & 400 to see how much the POI is different and then crunch the numbers in the ballistic calibration page of AB.

 

[alf]

I generally take a more simplistic approach.......

I tend to get a close enough zero at 200, then move directly to 600-800- or 1000, depending, and tweak my scope to match my drops at distance. I don't fret over being a click or two off at "close" range.

 

[Canadian bushman]

I generally take a more simplistic approach.......

I tend to get a close enough zero at 200, then move directly to 600-800- or 1000, depending, and tweak my scope to match my drops at distance. I don't fret over being a click or two off at "close" range.

+1

1 minute off at 800 will hurt a lot more that 1 minute off at 100 will.

 

[swampshooter]

My Nightforce 12-42X BR adjustments are not true. It should take 8 clicks for me to move 1" at 100 yds. (or 1 moa) and it takes 9. This has been verified numerous times out to 1,000 yds.