Range Report trouble with .308 ballistic

[wjusticed]

I was trying out the JBM system and i am hitting 6.5" high at 400 yards when i go by their calculations. I don't understand what I'm doing wrong. I dialed in 3.75 on my scope like JBM said. Can some one help me out? My zero is at 270 yards.
Thanks wjusticed

Trajectory
Input Data
Manufacturer: Barnes Description: Tipped Triple-Shock™ X Boattail
Caliber: 0.308 in Weight: 130.0 gr
Ballistic Coefficient: 0.350 G1

Muzzle Velocity: 3000.0 ft/s Distance to Chronograph: 15.0 ft

Sight Height: 2.00 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: 10.0 mph Target Angle: 90.0 deg

Temperature: 59.0 °F Pressure: 29.92 in Hg
Humidity: 0.0 lb/ft³ Altitude: 0.0 ft

Vital Zone Radius: 5.0 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
Output Data
Elevation: 6.617 MOA Windage: 0.000 MOA

Atmospheric Density: 0.07647 lb/ft³ Speed of Sound: 1116.5 ft/s

Maximum PBR: 353 yd Maximum PBR Zero: 302 yd
Range of Maximum Height: 171 yd Energy at Maximum PBR: 1289.0 ft•lbs

Sectional Density: 0.196 lb/in²
Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
0 -2.0 *** 0.0 *** 3014.2 2.700 2622.1 0.000 0.0 ***
50 1.0 1.9 0.2 0.4 2874.6 2.575 2384.9 0.051 9.0 17.1
100 2.9 2.8 0.9 0.8 2739.5 2.454 2166.0 0.104 18.4 17.5
150 3.6 2.3 2.0 1.3 2608.4 2.336 1963.6 0.161 28.3 18.0
200 3.1 1.5 3.6 1.7 2481.1 2.222 1776.6 0.219 38.6 18.4
250 1.2 0.5 5.8 2.2 2357.3 2.111 1603.8 0.282 49.5 18.9
300 -2.3 -0.7 8.5 2.7 2237.1 2.004 1444.3 0.347 61.0 19.4
350 -7.5 -2.1 11.9 3.2 2120.2 1.899 1297.4 0.416 73.2 20.0
400 -14.7 -3.5 15.9 3.8 2007.0 1.798 1162.5 0.488 86.0 20.5
450 -24.0 -5.1 20.7 4.4 1897.4 1.699 1039.0 0.565 99.5 21.1
500 -35.8 -6.8 26.2 5.0 1791.8 1.605 926.6 0.647 113.8 21.7
550 -50.2 -8.7 32.6 5.7 1690.4 1.514 824.7 0.733 129.0 22.4
600 -67.7 -10.8 40.0 6.4 1593.7 1.427 733.1 0.824 145.1 23.1

 

[Killswitch Engage]

Re: trouble with .308 ballistic

ditch that 270yd zero. that is a bad idea. why are you doing that anyhow?

it will be much easier for you to track your dope and return to zero with a 100yd zero on your gun. if you want it zeroed for 200yds or so just simply dial that on and leave it there.

it looks to me like the 270yd zero is not factored into the ballistic data which is why it doesn't match up.

 

[Killswitch Engage]

Re: trouble with .308 ballistic

and fill out your profile before the admin catches up to you.

 

[wjusticed]

Re: trouble with .308 ballistic

The reason i like the 270 zero. is for quick 0 to 300 yard shots on deer.
The 270 yard zero is figured in that's why it's 3" high at 100 yards.

 

[Lindy]

Re: trouble with .308 ballistic

Did you get that 270 yard zero by shooting at 270 yards, or by dialing up what a ballistic program said from a 100 yard zero, and then zeroing out the knob?

I'd be suspicious that your zero is off. I ran the calculations in another ballistic program, and they look OK, although you should have dialed up 3.5 MOA, not 3.75.

 

[wjusticed]

Re: trouble with .308 ballistic

i usually set my guns a little high at 100 yds. this time i sighted in 3" high at 100 yds. that ends up being zeroed at 270 yds. this works on my other guns.

I will check this zero this week to make shore. sorry for being a dumb ass, should have checked.

 

[Swan]

Re: trouble with .308 ballistic

Don't bother with JBM or any other ballistic software for ACTUAL dope. They are good for reference, but thats it. Drop some paper @ 300, 400, 500, 600yds, etc and let the results speak for themselves. Too many people get caught up in "adjusting jbm numbers" to match their real dope and its a gigantic waste of time... I speak from experience doing just this.

Just shoot, and record your results. That is Real Dope.

Peanut Gallery may correct me if I am incorrect...

 

[acttacus]

Re: trouble with .308 ballistic

I agree with Swan,

One should never rely solely on ballistic software, it provides only a prediction of the dope based on a set of given information.

In real life, many external factors will affect the actual dope of the bullet, and the only way to know the exact dope is to shoot at various distances and have a good record of the shots.

 

[Lindy]

Re: trouble with .308 ballistic

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Just shoot, and record your results. That is Real Dope.</div></div>

Indeed it is.

Ballistics programs often disagree with real dope. There are many sources of ballistic program inaccuracies..

However, if you have to go shoot at distances you've never shot before, or in an environment which is very different, a ballistics program can be a valuable resource to get you close on the first shot and you can get actual dope.

If you've never shot above sea level, and have to deploy to the Hindu Kush, it'd be a good idea to have the output of a ballistic program with numbers which will be close.

 

[wjusticed]

Re: trouble with .308 ballistic

Will do the the paper drop @300,350,400,ect. Thanks for the help!!

 

[azimutha]

Re: trouble with .308 ballistic

You're in NC but are you actually shooting at sea level? You're using a pressure corrected barometric pressure but leaving altitude @ 0. Go up 2000 feet and that'll give you about 10" right there. Also, how do we know the Barnes BC is correct? And ideally you'd have a G7 or G5 BC for a boattail. So while it's true even JBM can't perform miracles, you need the best data going in.

 

[deersniper]

Re: trouble with .308 ballistic

Yeah, 0% humidity and 0 ft altitude may have something to do with it.