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Need a drop chart

 
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  #8  
Old 02-05-2010, 12:54 PM
tlk tlk is offline
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Join Date: Apr 2008
Posts: 238
Re: Need a drop chart

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 Retard. Coeff. rate
1300 Break Velocity (fps)

Calculated data & constants:
0.502 Adjusted BC
4269 Retardation coeff.
4521 Adj. Retard. 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 by tlk; 02-05-2010 at 12:59 PM.
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  #9  
Old 02-05-2010, 06:48 PM
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Join Date: May 2007
Location: California
Posts: 458
Re: Need a drop chart

Try Big Game Info - A resource for the big game hunter It's not as fussy.
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  #10  
Old 02-06-2010, 12:11 AM
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Join Date: Nov 2008
Location: SW Montana
Posts: 4,257
Re: Need a drop chart

It looks like you may have two different BC's. I plugged it into Loadbase 3.0 and it agreed with JBM, I used a single BC of .409, if I lay a track along side with a BC of .474 it put a .7 MOA difference.

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  #11  
Old 02-06-2010, 01:39 PM
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Join Date: Jul 2008
Location: Billings, MT
Posts: 50
Re: Need a drop chart

Berger has a new Ball calc also..
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  #12  
Old 02-07-2010, 08:53 AM
tlk tlk is offline
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Join Date: Apr 2008
Posts: 238
Re: Need a drop chart

I Used JBM and Big Game Info for shots at 400 yesterday. Everything worked out.

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.
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  #13  
Old 02-07-2010, 02:52 PM
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Join Date: Nov 2008
Location: SW Montana
Posts: 4,257
Re: Need a drop chart

I used .409 because it is middle of the road. Sierra uses three BC's but I did not know that JBM would use three but it kinda looks that way. JBM also lists Litz's BC for that bullet and I have found that to be very accurate but I don't know what it is, I'm going to get his book on order ASAP.
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.
Warm up your Ballistics Calculator!
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