Computed Ballistic Data vs Actual=Perplexing

[BD100]

Gents,

I went to the range yesterday to verify drops/trajectory out to 500 yds utilizing a load for my new 240 Weatherby. I'm planning to order a custom dial for my Leupold scope and simply wanted to verify computed vs actual drops. I anticipated a small delta between the two, but was surprised to find they were substantially different. The actual's were much flatter than what JBM's on-line calculator came up with. My load utilizes a 95gr Nosler Ballistic Tip at 3450fps. The velocity was verified with my chronograph.

Below is what I came up with utilizing a 100 yd zero and the average drop of 4 shots at each distance from 100-500 yds. I've seen small discrepancies before, but never any this large.
It was a little windy during the range session, but it was primarily a quartering head-wind of about 10-12mph, which I figured would increase the drop just a skosh.



JBM Actual

100 0 0
200 -1.9 -1.0
300 -7.9 -3.0
400 -18.6 -13.5
500 -35.0 -25.5

Have any of you folks seen a difference this large between computed and actual drops? After seeing this, I'm just a little concerned the dial Leupold sends won't be very accurate. It's my understanding they take your actual muzzle velocity(if you know it), bullet BC, avg temp, elevation
and create a dial. If this is the case, mine will be wayyy off. What do guy's think?

 

[dcali]

Your inputs are incorrect. Try running the numbers again. At 500 yards JBM should be within 1/2 MOA or better.

 

[BD100]

Your inputs are incorrect. Try running the numbers again. At 500 yards JBM should be within 1/2 MOA or better.

I don't believe that is the problem. I also used Hornady's and Handloads.com's calculators and came up with very similar data to JBM.

 

[boltfluter]

+1 for a wrong input. Been there and done that myself. If your inputs turn out to be correct I would suspect your chrono for giving faulty readings. Good luck.

Paul

 

[STOMP442]

Make sure you are using the correct BC G1 or G7. make sure your scope height is correct and also make sure that your reticle is properly aligned. Perform a tall target test and verify that the clicks on your scope are moving the correct amount and in a verticle line.

 

[Fast14riot]

A 0.379 G7 matches your actual much closer than a G1 of the same number...

 

[Delfuego]

Check the box in JBM labeled "Std. Atmosphere At Altitude" and manually enter your BC. See if it looks a little closer.

 

[savagedasher]

+1 for a wrong input. Been there and done that myself. If your inputs turn out to be correct I would suspect your chrono for giving faulty readings. Good luck.

Paul

Garbage in garbage out .
If you don't have a control system nothing comes out . Any Changes in the information being put in will change the results .
Biggest change would be dealing with bul

+1 for a wrong input. Been there and done that myself. If your inputs turn out to be correct I would suspect your chrono for giving faulty readings. Good luck.

Paul

 

[seymour fish]

Garbage in garbage out .
If you don't have a control system nothing comes out . Any Changes in the information being put in will change the results .
Biggest change would be dealing with bul

Leupold scope !!!!! Set up a yardstick at 100. Heavily bag the gun. Dial the windage knob and notice your 0.25 MOA clicks are actually 0.33 MOA. Send it back to Leopold, and they will tell you it's perfect.

 

[Webster]

Gents,

I went to the range yesterday to verify drops/trajectory out to 500 yds utilizing a load for my new 240 Weatherby. I'm planning to order a custom dial for my Leupold scope and simply wanted to verify computed vs actual drops. I anticipated a small delta between the two, but was surprised to find they were substantially different. The actual's were much flatter than what JBM's on-line calculator came up with. My load utilizes a 95gr Nosler Ballistic Tip at 3450fps. The velocity was verified with my chronograph.

Below is what I came up with utilizing a 100 yd zero and the average drop of 4 shots at each distance from 100-500 yds. I've seen small discrepancies before, but never any this large.
It was a little windy during the range session, but it was primarily a quartering head-wind of about 10-12mph, which I figured would increase the drop just a skosh.



JBM Actual

100 0 0
200 -1.9 -1.0
300 -7.9 -3.0
400 -18.6 -13.5
500 -35.0 -25.5

Have any of you folks seen a difference this large between computed and actual drops? After seeing this, I'm just a little concerned the dial Leupold sends won't be very accurate. It's my understanding they take your actual muzzle velocity(if you know it), bullet BC, avg temp, elevation
and create a dial. If this is the case, mine will be wayyy off. What do guy's think?

Forget the computer data. The range data is the real stuff. Cancel your order and give them the actual range data. Don't understand the big difference. If you manipulate the numbers to force the data to match range data you have not gained anything.

 

[Brians356]

If you manipulate the numbers to force the data to match range data you have not gained anything.

That's what so-called climate scientists do "improve" their global temperature forecast models. Works for them, just ask 'em.
-

 

[Zero333]

Is your "Actual" drop a guesstimate from the amount you dialed ? or...

Did you have a 4 foot target at 500 yards, aimed to the top of it, and the bullet impact was 25.5" from point of aim ?

 

[BD100]

Is your "Actual" drop a guesstimate from the amount you dialed ? or...

Did you have a 4 foot target at 500 yards, aimed to the top of it, and the bullet impact was 25.5" from point of aim ?

No, it wasn't a guesstimate. I actually zeroed at 100 and then used a large piece of cardboard with a bullseye at the top and moved it to 200,300,400 and 500 yds.

 

[BD100]

Forget the computer data. The range data is the real stuff. Cancel your order and give them the actual range data. Don't understand the big difference. If you manipulate the numbers to force the data to match range data you have not gained anything.

I haven't ordered the dial yet. I'm going to re-shoot at all distances to verify my original drops. If they're the same, I'll order the dial and provide Leupold with my actual range data.

 

[BD100]

Leupold scope !!!!! Set up a yardstick at 100. Heavily bag the gun. Dial the windage knob and notice your 0.25 MOA clicks are actually 0.33 MOA. Send it back to Leopold, and they will tell you it's perfect.

Yes, I'm a little skeptical of the newer Leupold scopes. I received such a great deal, I couldn't pass it up.

 

[Willie]

What was your chronograph setup?

 

[dcali]

I don't believe that is the problem. I also used Hornady's and Handloads.com's calculators and came up with very similar data to JBM.

If the inputs are correct, then you are measuring something wrong. You need to figure out which thing is wrong. Nosler is not exactly well known for reporting accurate BC's, but you'd assume theirs would be too high. Check range and velocity. Those are usually the culprits. BC is the other big one, but that's not exactly easy to test. Are you at sea level?

 

[BD100]

If the inputs are correct, then you are measuring something wrong. You need to figure out which thing is wrong. Nosler is not exactly well known for reporting accurate BC's, but you'd assume theirs would be too high. Check range and velocity. Those are usually the culprits. BC is the other big one, but that's not exactly easy to test. Are you at sea level?

I'm using a Competition Electronics Pro Chronograph, which has proven to be fairly accurate. Additionally, my muzzle velocity is very close to what Quickload computes. I've compared JBM's data to other on-line ballistic calculators and they're all really close, so I don't believe my inputs are incorrect. If somebody wants to check it out, here is my data..

95 gr NBT= .379 G1
MV-3450
Distance to Chrono-12 ft
Sight Height-1.5 in
Wind speed =10mph
Wind Angle= 180
Zero Range=100 yds
Temp=80f
Baro Psi=29.82
Altitude=600 ft

 

[savagedasher]

And when it all done H2O grains water determined the final results along with altitude . Larry

 

[SheepDog]

Is the center of your scope really 1.5" from the centerline of the bore? I know that 1.5 is the "standard" but I also know that my scopes are higher than 1.5 on all my rifles.