Does anyone know of a online ballistic program other than JBM? I am trying to run some long range trajectory calculations and have run into a snag. I am shooting a 7stw @3525 fps with a 130 grain bullet. Zeroed at 100 yd this round will be 2.5" high at 200 yds and 4.5" low at 300 yds. I am trying to calculate drop at 400, 500, 600, etc. My problem is that the JBM program assumes a zero that appears to be the "high point" in the bullet path. The way I understand bullet path is that the bullet will cross the line of sight twice (with my load it is at 100 and some point between 200-300). The JBM program shows a path that peaks at a 100 yd zero and then begins to fall. What am I doing wrong? My BC is .550 with a G5 drag curve. Any help would be appreciated.

See if this will help.

http://internet.cybermesa.com/~jbm/ballistics/traj/traj.html

Andrew V. McGee

I am not sure what you are doing there Big John. I have used JBM a lot and it has been right on for me. Are you using the HV bullet from Gerard? You are right that you should have 2 points in your trajectory that the bullet passes through the line of sight. If you tell it to Zero at 100 and then tell it you want your zero to be 3" high at this range it will show you something that kind of resembles what you are saying but it will still show two intersections in your trajectory. I always just tell it to zero at a mid point like 326 for my 7 STW. This will give me dead on at 326 and then show high or low for all other ranges.
Vince

Maybe this will help Big John. This is from JBM. I didn't know your scope height or your altitude so I just used 1.5 and 1500 ft.
Trajectory Output

--------------------------------------------------------------------------------

Input Data
Muzzle Velocity: 3525.0 ft/sec
Chronograph Distance: 10.000 feet
Ballistic Coefficient: 0.550
Drag Function: G5
Bullet Weight: 130 grains
Sight Height: 1.50 inches
Sight Offset: 0.00 inches
Wind Range Speed: 0 mph
Wind Vertical Speed: 0 mph
Wind Cross Speed: 10 mph
LOS Angle: 0 degrees
Cant Angle: 0 degrees
Target Speed: 10 mph
Target Angle: 90 degrees
Zero Range: 250 yards
Zero Height: 0 inches
Zero Offset: 0 inches
Temperature: 53.7 �F
Barometric Pressure: 28.33 in Hg
Relative Humidity: 0.0 %
Altitude: 1500 feet
Air Density: 96 % of Sea Level

--------------------------------------------------------------------------------

Calculated Table
Elevation: 4.102 moa
Azimuth: 0.000 moa

Range Velocity Energy Momentum Drop Windage Lead Time
(yards) (ft/sec) (ft-lbs) (lbs-sec) (inches) (inches) (inches) (sec)
0 3528.7 3594.1 2.04 -1.5 0.0 0.0 0.000
50 3473.3 3482.2 2.01 0.3 0.1 7.5 0.043
100 3418.2 3372.6 1.97 1.4 0.2 15.2 0.086
150 3363.5 3265.5 1.94 1.7 0.5 23.0 0.131
200 3309.1 3160.7 1.91 1.2 1.0 30.9 0.176
250 3255.0 3058.3 1.88 -0.0 1.5 38.9 0.221
300 3201.3 2958.2 1.85 -2.1 2.2 47.1 0.268
350 3147.9 2860.3 1.82 -5.0 3.1 55.4 0.315
400 3094.8 2764.7 1.79 -8.7 4.1 63.9 0.363
450 3042.1 2671.3 1.76 -13.4 5.2 72.5 0.412
500 2989.7 2580.0 1.73 -19.1 6.5 81.3 0.462
550 2937.7 2491.0 1.70 -25.7 7.9 90.2 0.512
600 2885.9 2404.0 1.67 -33.3 9.5 99.2 0.564
650 2834.6 2319.2 1.64 -41.9 11.2 108.5 0.616
700 2783.6 2236.5 1.61 -51.7 13.1 117.9 0.670
750 2732.9 2155.8 1.58 -62.5 15.2 127.4 0.724
800 2682.6 2077.2 1.55 -74.5 17.5 137.2 0.779
850 2632.7 2000.6 1.52 -87.7 20.0 147.1 0.836
900 2583.1 1926.0 1.49 -102.2 22.6 157.2 0.893
950 2533.9 1853.3 1.46 -118.0 25.4 167.6 0.952
1000 2485.1 1782.7 1.43 -135.1 28.5 178.1 1.012

Big John

Basically this is how Near and Far zero relate. As the Far zero move further from the shooter the near zero moves closer.

With the load data you've given and using a 1.5 scope height and the height of the round at 250 yards your near zero is about 30 yards, not 100.

The only way to have a near zero at 100 yards is to sight for something very close to 100, somewhere in the 110 yards range.

BUT, if you use a scope mount that puts the centerline of the scope 5.5 inches above the bore you'll have a Near zero at about 100 yards and still be 2.5 inches high at 250 yards, your Far zero for this setup would be 340 yards and you'll be 3.4 inches low at 400 yards.

I had the same issue. .. if you have MS-Excel
spreadsheet software, download the freeware from: http://www.jacksonrifles.com/ballistics.htm
by Pejsa.

Good Luck,
Jeff
www.woodybros.com

Try PointBlank - visit www.huntingnut.com a download it free

Here's another MS Excel spreadsheet or two.

Try the Sniper version or the RBC (Ranging Ballistic Computer) version.

They're free and not password protected so uou can modify them as you like.

They can be downloaded to a handheld computer like the Casseopia and used in the field. The RBC version can be used to calculate Target Reference Point distances via GPS input and automatically figures ALL single field wind values from a single vector input.

Dave King:

Could you please state where such excel spreadsheets can be downloaded?

Thanks, Antonio

Have you tried the on-line ballistic program at the Norma website? You can input all variables such as sight height, B.C., bullet weight, velocity, etc., and it will show trajectory out to 600 yards and height of tragetory above or below line of sight at any point from muzzle on out.

go to
www.norma.cc/normawebNY/index.htm
then choose "Ballistics"

Sorry guys!

got carried away with an immediate problem and forget to paste the link.

The Spreadsheet is on Peter Cronhelm's pages.

http://www.nucleus.com/~cronhelm/ballistics.html

Forgive me for my forgetfullness..