Data not matching shooting

[JustAGuy]

So I finally had a chance to take a poke at the 500 yd steel at the Cheyenne Mountain Shooting Complex yesterday.

I've used both JBM ballistics calculator and the excel spreadsheet provided by meccastreisand on YouTube as well as the spreadsheets
by Tiborasorus Rex. All three data sources have indicated that with my load, I had 2.6 Mils of drop at 500 yards. The actual shooting
proved that I needed closer to 5 Mils of adjustment. I've double checked my inputs for the programs and all seems to be good.

Any ideas on why my actual drops are so far off from my data?

s

[ray1970]

Lots of variables here. First, have you chronographed your load? Guessing or assuming a loads velocity off published data can throw things off.

[Trigger Time 23]

That's is where I would start as well. Chrono the round you are using to verify velocity.

[Hoser]

You dont need a chrono.

Get a rock solid zero at 100.

Then figure out how much drop you are getting at 300. Select your bullet in a ballistic program and do the match backwards to find out how fast the bullet is going. You might need to tweak it some more out past 800 or so. It will get you within a couple inches out past 600.

[Tim K]

What load?

If 2.6 is really right for 500, 5.0 should get you close to 800.

[JustAGuy]

Yep, have chrono'd this particular load with an average velocity of 3296 fps, averaged over more than 100 measured rounds. ES over that 100 rounds is just under 32 FPS as these are all hand trickled loads.
And while I know that this load is not really appropriate for longer range shooting, it's what I had handy and what I worked up the data for before I went to the range yesterday. The load is 40 Gr VMax over 25.7
gr IMR 8208 XBR.

I know something has to be out of whack with my inputs since the 5 mil drop was getting me hits every time on the 500 yd steel.

S

[Tim K]

A quick run through my app gave 3.0 mils to 500. Something is definitely goofy. 100 yard zero?

[JustAGuy]

Yep, 100 yd zero. Maybe time to get that scope in your jig? It has recovered from the trauma sustained last year.

Sam

[TheBelly]

What is the height over bore of the centerline of the optic?

[JustAGuy]

3 inches. Scope is a Falcon Menace 4-14 X 44. It's a little higher than I'd like it but it's the best I can do right now.

s