True BC of 338 Berger 300gr OTM

[Grizzdude]

I'm trying to find the true BC of the berger 300gr bullets. When I input .818 in my ballistic program it is way off. So far I know the bullet drops 1.1mil at 285 yards and 16.2mil at 1 mile 1760 yards. I am using 90gr h1000 that I believe is pushing the bullet 2700 fps. When it was sunny my fps were showing 2785 avg, when a big cloud past over the same loads read 2705 avg. I'm using the alpha master chrono, I believe the 2705 fps is more correct because someone else with the same rifle was getting the same 2700 fps with 90gr h1000 pushing the bergers. So using 2700 fps and lowering the BC to .735 puts 1.1mil at 285 yards and 16.2 mil at 1760 yards. There is an option to put in lower bc followed by lowest bc but I haven't found those numbers for the 300gr bergers. Just wondering what the heck is going on? I doubt the GPS is giving me a false reading. These calculations are at an altitude of around 7000 ft , at 85 F , RH 50%.

Just tried the online jbm calculator and it is right on with .818bc with a 2740fps. Looks like my ballistic programs are crap and my chrono isn't too on par with the actual fps.

 

[Beluebow]

Have you tried using the G7 BC instead of G1?

 

[LawnMM]

I too have fallen victim to the ballistic calculator not adding up to actual data. Here are some of the factors I've found.

-Your chronograph may be off by a few fps, doesn't have to be much at ELR distances to make a difference
-You may be telling your ballistic calculator the speed the chronograph read at the CHRONO, not the muzzle
-If your Chrono is sensitive to light changes, infra-red screens may help by giving a consistent light source
-The BC of the bullets may be off, the drop test method is apparently much more accurate for calculating BC
-Scope tracking accurately? Have you done a tracking test?

My solution was changing ballistic apps, so far on paper the new one has been spot on without me having to lie to it and cheat my way to the correct answer

 

[USAS]

Do you have a truing function in your ballistic program?.