Plotting a Graph from Known Drop Points?

[Stugotz]

O.K., I'm a little new to this, so any help would be appreciated. This is my first post, but I've been lurking around for a while. I've tried a few of the "freeware" ballistic programs and an Excel spreadsheat that I found on another site in addition to the trial version of RSI's Ballistics program, but none of these seem to calculate the correct curve for my particular rifle and load. I'm shooting a 7mm RUM with 26" Douglas barrel. 139 grain Hornady SST's on 93.5 grains of Reloader 25. at 3465 FPS 15 feet from muzzle. One of the programs I'm using corrects this velocity to 3476 at the muzzle, so I've been using that number as muzzle velocity. I'm at about 975 feet above sea level and it's been about 50 degrees here. From shooting at various distances, I've determined that I'm +2.5in.@100Yds, +1.75in.@250, -10in.@400, and -14in.@450. The rifle also has a 20MOA one piece incline base on it, and I'm not sure if this is a factor. Heigth of the scope at the front bell is 1.828 center of bore to center of tube. Now for the question. Is there any way to take these 4 points and plot a graph where I can see drop every 10 feet from 100 Yds to 1000. Sorry this was so long, but thanks in advance for your help.

 

[Ian M]

If you are going to hunt with the rifle you will probably not need a drop-chart in 10 foot or even ten yard increments. Maybe the 1000 yard shooters would use one that fine but we have determined that 25 yard increments work great. We shoot our drops on paper. Did that before deer season all the way out to 650 which is as far as we would shoot with our rigs.
There are no doubt computer programs which will do what you need, check EXBAL as it seems to be very popular with guys here. Do a search for Perry Systems and EXBAL and you will find their site.
Good luck with your shooting.

 

[Stugotz]

Sorry, typed that wrong, meant 10 YDS, but i'm sure 25 would be more than enough. Trouble is, I don't have enough flat land where I live to shoot at all the distances that are available where I'm planning on hunting. Don't think I'll take any shots past the 450yds I shot at today, but need some idea of where I'm at between 250 and 400yds. Guess I'll keep adjusting BC's 'till i get something to resemble my known drops.

 

[Perkules]

Hello Stugotz,

I played around with a program for a while, adjusting the velocity only. Velocity can often be the guesswork after all. I was able to duplicate your path quite well with the MV being 3450 and zeroed at 290 yds, everything else being equal.

I would trust the BC -based trajectory with the shooting you have done rather than tweak the BC.

Close enough to get an idea,I hope.


0 3450 3675 0,000 -1,82
25 3389 3546 0,021 -0,54
50 3330 3423 0,044 0,55
75 3272 3305 0,066 1,45
100 3214 3189 0,09 2,15
125 3158 3079 0,113 2,63
150 3103 2973 0,137 2,90
175 3049 2870 0,161 2,94
200 2995 2769 0,186 2,75
225 2943 2674 0,212 2,32
250 2892 2582 0,237 1,63
275 2841 2492 0,263 0,69
300 2791 2405 0,29 -0,52
325 2743 2323 0,317 -2,01
350 2695 2242 0,345 -3,79
375 2647 2163 0,373 -5,87
400 2601 2089 0,401 -8,26
425 2556 2017 0,43 -10,97
450 2511 1947 0,46 -14,01
475 2467 1879 0,49 -17,39
500 2424 1814 0,521 -21,14
525 2382 1752 0,552 -25,24
550 2340 1690 0,584 -29,74
575 2299 1632 0,616 -34,63
600 2259 1575 0,649 -39,93

Man,I hope this shows properly.

 

[Perkules]

It does!

Left to right: Distance,Velocity,Energy,Time Of Flight,Drop.

I left wind drift etc. out so it is readable.

EDIT: Yes,this is the 7mm Hornady 139 grain SST ,BC .486. Better shoot some more groups in those 250 to 400 distances before hunting, this can be all wrong after all.

It´s the only sure way. Good luck,hope this helps.

[ 11-18-2003: Message edited by: Petander ]

 

[Stugotz]

Thanks Petander!!! What program did you use to get these results? Do you know which drag function it uses (G1,G5,G7)?

 

[700]

Stugotz

I do not douth your MV of 3476fps or your value of 2.5 inches high at 100 yards. 100 Yards is quite close to your shooting position and so the effect of errors is limited.

Taking these values and a G1 BC of 0.486 I got the following drop table:-

Range Yrds,Range Mts,Velocity Ft.S-1,Energy Ft.Lb,Momentum Lb.S,Drop In,Drop CM
0,0,3476.03,3729.09,2.1456,-1.828,-4.64312
25,22.86,3421.16,3612.29,2.11173,-0.462704,-1.17527
50,45.72,3366.97,3498.77,2.07829,0.716986,1.82114
75,68.58,3313.45,3388.41,2.04525,1.70505,4.33082
100,91.44,3260.56,3281.11,2.0126,2.49524,6.33791
125,114.3,3208.31,3176.78,1.98035,3.08109,7.82598
150,137.16,3156.66,3075.33,1.94847,3.45589,8.77797
175,160.02,3105.61,2976.67,1.91696,3.61268,9.17621
200,182.88,3055.15,2880.72,1.88581,3.54423,9.00234
225,205.74,3005.25,2787.39,1.85501,3.24303,8.23729
250,228.6,2955.92,2696.63,1.82456,2.7013,6.86129
275,251.46,2907.14,2608.35,1.79445,1.91093,4.85376
300,274.32,2858.89,2522.5,1.76467,0.863516,2.19333
325,297.18,2811.18,2439.01,1.73522,-0.449695,-1.14223
350,320.04,2763.99,2357.81,1.70609,-2.0378,-5.17602
375,342.9,2717.32,2278.86,1.67728,-3.91027,-9.9321
400,365.76,2671.16,2202.09,1.64879,-6.07696,-15.4355
425,388.62,2625.5,2127.46,1.62061,-8.54813,-21.7122
450,411.48,2580.35,2054.91,1.59274,-11.3344,-28.7895
475,434.34,2535.68,1984.38,1.56517,-14.4471,-36.6955
500,457.2,2491.51,1915.85,1.5379,-17.8975,-45.4598
525,480.06,2447.82,1849.25,1.51094,-21.698,-55.1129
550,502.92,2404.62,1784.55,1.48427,-25.861,-65.687
575,525.78,2361.9,1721.7,1.4579,-30.3998,-77.2155
600,548.64,2319.65,1660.66,1.43182,-35.328,-89.7332
625,571.5,2277.88,1601.38,1.40603,-40.66,-103.276
650,594.36,2236.58,1543.84,1.38054,-46.4107,-117.883
675,617.22,2195.62,1487.81,1.35526,-52.5957,-133.593
700,640.08,2154.93,1433.19,1.33015,-59.2314,-150.448
725,662.94,2114.64,1380.09,1.30527,-66.3349,-168.491
750,685.8,2074.75,1328.52,1.28065,-73.9243,-187.768
775,708.66,2035.29,1278.46,1.2563,-82.0185,-208.327
800,731.52,1996.27,1229.92,1.23221,-90.6372,-230.218
825,754.38,1957.72,1182.87,1.20841,-99.8011,-253.495
850,777.24,1919.63,1137.29,1.18491,-109.532,-278.211
875,800.1,1882.04,1093.18,1.1617,-119.852,-304.425
900,822.96,1844.94,1050.51,1.1388,-130.786,-332.197
925,845.82,1808.35,1009.25,1.11622,-142.359,-361.591
950,868.68,1772.28,969.39,1.09395,-154.595,-392.672
975,891.54,1736.73,930.892,1.07201,-167.524,-425.511
1000,914.4,1701.71,893.731,1.05039,-181.173,-460.18

With values corrected for your altitude and temperature.

These values were confirmed by two seperate programs which only showed a difference of 1 inch at 1000 yards.

At ranges other than 100 yards, my drops are out of whack with yours. At 400 yards you get a drop of 10 inches and my tables show 6 inches.

Perhaps some thing you could check for is canting. This may be due to the scope not being aligned properly on the vertical/horizontle axis or maybe you are holding the rifle at a slight angle. Canting will cause point of impact error which increase exponentially at longer ranges.

Another thing to check is are the given distances correct. My tables give 6 inches drop at 400 and 10 inches drop at 450 yards. 10 inches is the drop you give at 400 yards. Perhaps your range measurments might be off.

If you email me at [email protected] I will send you a chart showing the drops given above.

Rgds

700

[ 11-20-2003: Message edited by: 700 ]

 

[ncharter]

Have you tried the JBM website. It is easy to use, gives you everything that you could want and best of all it is free....
http://www.amasci.com/~jbm/ballistics/ballistics.html

 

[Stugotz]

Guess what, when I posted those drops, I looked at the wrong entry from my notes, as it turns out, I am 6" low at 400 Yds. all the other drops I listed are correct, but the 450 Yd drop of 14" is actually at 458yds. These look pretty close to the above chart. I'm using a laser range finder which I assume is fairly accurate, but I have not checket it, and I am using a base mounted level to keep things straight. Thanks for all the info, I'm going back now and running the programs again to see what I come up with.

 

[Perkules]

Yep,the 400 / 450 was the biggest problem. Please report the results when you go shooting, this is always interesting.

 

[Perkules]

No prob!

G1...?... sorry,I don´t know. But here it is, "Ballistic Basics" with a different zero and some drift for your load:

Again,all this must be confirmed in real life. Means lots of shooting.

But I like playing with these,here you can find a couple:

Eskimo

 

[700]

Stugotz

Check your email.

Rgds

700