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- Thread starter tlk
- Start date

Help Support Long Range Hunting Forum

or you can use the excellent free one at JBM here:

JBM - Calculations

Hope this helps!

Brian

I used the JBM site and what I am needing is a chart that tells me how many MOA I need to dial in for elevation. Is the Drop(MOA) column that information?

What I was looking for was something like: 300 yards, +2.5 MOA.

Lot of info there on the JBM application.

I used the JBM site and what I am needing is a chart that tells me how many MOA I need to dial in for elevation. Is the Drop(MOA) column that information?

YES. YOU ARE RIGHT ON..

If you change the value to MIL you will get the dial in MIL.

Just as info, if you do not know what to do with JBM at a specific field input just click on the "?" attached to this particularly field. You will jump to a help page.

I like it cause I can take my laptop out and use it and don't have to worry about having internet conncetion to get to JBM.

When I run JBM and Jacksonrifles.com against each other I get 1.2 MOA difference at 600 yards. I thought I would see differences, but that seems extreme. I was careful to enter the exact data in both, including elevation, wind, pressure, etc.

What gives? Since it SHOULD all be science by now, I would think that any error would be rounding and minimal.

If you post up your data we could have a look at it. I'm running Loadbase 3.0 and out to about 1000yrds JBM is fairly close if I have everything spot on, maybe give you some more perspective.

JBM:

Manufacturer: Sierra

Description: Spitzer Boattail (GameKing)

Caliber: 0.308 in

Weight: 165.0 gr

Ballistic Coefficients: 0.419 [0-1600], 0.409 [1600-2400], 0.404 [2400-5000]

G1 Muzzle Velocity: 2983.0 ft/s

Distance to Chronograph: 10.0 ft

Sight Height: 1.50 in

Sight Offset: 0.00 in

Zero Height: 0.00 in

Zero Offset: 0.00 in

Windage: 0.000 MOA

Elevation: 0.000 MOA

Line Of Sight Angle: 0.0 deg

Cant Angle: 0.0 deg

Wind Speed: 10.0 mph

Wind Angle: 90.0 deg

Target Speed: 0.0 mph

Target Angle: 90.0 deg

Temperature: 70.0 °F

Pressure: 29.92 in Hg

Humidity: 75.0 %

Altitude: 1047.0 ft

Vital Zone Radius: 2.0 in

Std. Atmosphere at Altitude: No

Pressure is Corrected: Yes

Zero at Max. Point Blank Range: No

Target Relative Drops: Yes

Mark Sound Barrier Crossing: No

Include Extra Rows: No

Column 1 Units: 1.00 in

Column 2 Units: 1.00 MOA

Round Output to Whole Numbers: No

Jacksonrifles.com:

Sierra 165 GKBullet description

2983 Muzzle speed (fps)

165 Bullet wt (gn)

0.474 BC1

00 Special range (yd)

0 Start range (yd)

50 Increment (yd)

0.00 Impact Ht. (in)

100 at Zero range (yd)

10 Wind speed (mph)

3.0 Wind dir. (o'clock)

20 Temp. (Celcius)

1047 Altitude (feet)

1000 Pressure (mbar)

1.50 Scope Ht. (in)

1.05 in./MOA @ 100 yds

0.50 ******. Coeff. rate

1300 Break Velocity (fps)

*Calculated data & constants:*

0.502 Adjusted BC

4269 Retardation coeff.

4521 Adj. ******. Coeff.

1000 Standard pressure

246 Mayewski constant

68 Temp. (Faht.)

2.04 Drop at Zero

I found part of the issue - Jacksonrifles.com has the temp in celcius. Have to jack it down to get it to where you want it in Farenheit (sp?). Still have .7 MOA delta at 600, though.

Thanks for your help - it is much appreciated.

Manufacturer: Sierra

Description: Spitzer Boattail (GameKing)

Caliber: 0.308 in

Weight: 165.0 gr

Ballistic Coefficients: 0.419 [0-1600], 0.409 [1600-2400], 0.404 [2400-5000]

G1 Muzzle Velocity: 2983.0 ft/s

Distance to Chronograph: 10.0 ft

Sight Height: 1.50 in

Sight Offset: 0.00 in

Zero Height: 0.00 in

Zero Offset: 0.00 in

Windage: 0.000 MOA

Elevation: 0.000 MOA

Line Of Sight Angle: 0.0 deg

Cant Angle: 0.0 deg

Wind Speed: 10.0 mph

Wind Angle: 90.0 deg

Target Speed: 0.0 mph

Target Angle: 90.0 deg

Temperature: 70.0 °F

Pressure: 29.92 in Hg

Humidity: 75.0 %

Altitude: 1047.0 ft

Vital Zone Radius: 2.0 in

Std. Atmosphere at Altitude: No

Pressure is Corrected: Yes

Zero at Max. Point Blank Range: No

Target Relative Drops: Yes

Mark Sound Barrier Crossing: No

Include Extra Rows: No

Column 1 Units: 1.00 in

Column 2 Units: 1.00 MOA

Round Output to Whole Numbers: No

Jacksonrifles.com:

Sierra 165 GKBullet description

2983 Muzzle speed (fps)

165 Bullet wt (gn)

0.474 BC1

00 Special range (yd)

0 Start range (yd)

50 Increment (yd)

0.00 Impact Ht. (in)

100 at Zero range (yd)

10 Wind speed (mph)

3.0 Wind dir. (o'clock)

20 Temp. (Celcius)

1047 Altitude (feet)

1000 Pressure (mbar)

1.50 Scope Ht. (in)

1.05 in./MOA @ 100 yds

0.50 ******. Coeff. rate

1300 Break Velocity (fps)

0.502 Adjusted BC

4269 Retardation coeff.

4521 Adj. ******. Coeff.

1000 Standard pressure

246 Mayewski constant

68 Temp. (Faht.)

2.04 Drop at Zero

I found part of the issue - Jacksonrifles.com has the temp in celcius. Have to jack it down to get it to where you want it in Farenheit (sp?). Still have .7 MOA delta at 600, though.

Thanks for your help - it is much appreciated.

Last edited:

Try Big Game Info - A resource for the big game hunter It's not as fussy.

Berger has a new Ball calc also..

BUT - I have question: Bigngreen, why did you use the BC of .409? Doumentation in Point Blank has a BC of .474, which is what I used. When I look at the JBM info I posted below I see that there are three different BC's (based on velocity, I assume, please correct if wrong). Based on what you found, I am wondering if this is where the difference I am seeing can be traced to.

Is JBM calculating based on different BC's at different bullet speeds during flight?

Thanks.

If I used .409 in Loadbase and the library file in JBM they were within a 1/10th at 600yrds. With Loadbase I can lay out multiple tracks next to each other so I used .409 for one and another at .474 and they where .7 apart in the same manner, it sounds like you had.

I started this thread, feel free to take a run at it with JBM it is good practice and for fun.

http://www.longrangehunting.com/forums/f19/warm-up-your-ballistics-calculator-52033/