modifications to GNU ballistics program

[popper]

Purpose is to determine the actual sight ANGLE of a 'golden' load to compare with other experimental loads. Sighting a rifle with the golden load (tested and verified fps - POI). Then compare (simulate) other loads, with known BC and fps. Object is to save time/$ and get an idea of the 'cone of fire' at different ranges (less than 100 in my case).
so far it appears BC has very little to do with POI for HV stuff. Change BC, sight angle and POI don't hardly change.

Program to calculate the real sight angle for a given load.
All are 30 cal, which makes no difference in the program.
bore to sight height angle (for 100 yds) is really small,

input is 2300 fps, 1.5" sight height. 100 yd zero.

125gr sst
input BC: .305
angle :0.172245
POI: 0.146728

150ssp
input BC: .388
angle :0.172245
POI: 0.146917

110 vmax
input BC: .29
angle :0.172245
POI: 0.146682

145 cast 31-142D mould
input BC: .22 a guess!!
angle :0.172245
POI: 0.146389

 

[popper]

Other than being bored, my experience shooting shows a discrepancy between expected results (on the target) and real results. Last results @ 100 a high BC bullet and RFN cast had close to same POI! Fps diff was 100 fps. Plus cast had a 4" vertical string. Test rifle is CVA SS BO using caldwell stand and rear bunny ear bag. Barrel is thicker than an HBAR so really rigid but not exactly free floated. GNU ballistics code has a few bugs, gravity doesn't effect horiz motion. Drag (air) has an effect on vert motion but very little at the low vertical fps.
Results:

***** results for Hornady 150spp (3031 pn) ******
rifle zero 100 yds, calculate ZAngle G1 drg.
*********** ZAngle: .172245 BC = .388 +/- 0.1 fps 2000
fps 100 yds POI fps vert.
1855.73, 99.1602, 0.39504, 0.788825
1818.82, 99.1586, 0.389991, 0.677261
1758.75, 99.1558, 0.381136, 0.490851
*********** ZAngle: .172245 BC = .388 fps 2000 +/- 50
fps 100 yds POI fps vert.
1866.35, 99.1586, 0.408225, 0.934087
1818.82, 99.1586, 0.389991, 0.677261
1770.85, 99.1585, 0.369432, 0.404518
Conclude +/- 50 fps or 0.1 BC change has almost NO effect on POI
and vertical fps is positive, bullet still rising. Drag 'force' is high at the muzzle and ~1/2 that at terminal fps.
So (other than my shooting) the vertical stringing? I'll get Sil to bring my led sled back for better shooting?
I know it's a simulation but so far, under 100 yds, BC and small variations in fps have no effect. And my fps calcs are essentially the same as hornady, sierra and other calculators.

 

[Ian]

Calculated predictions and actual shooting differ greatly at only 100 yards because of the human being supporting the rifle. Predictive programs to not account for recoil vibrations and muzzle rise AFAIK,

 

[popper]

True. human being supporting the rifle, like ME.

 

[popper]

So far, simulation and targets say 1300-2k fps, any BC but a flying coke can good to 50 and slowest gives a slight drop past 75 yds. Tested cast and jacketed in BO. Sight 1/2" high @ 50 and good to go.

 

[popper]

tested today, cva @ 100 and then 50. 20-25 mph headwind.
1)150spp 2k fps, BC .388.
2) 110 hj CFE pistol 1500 BC .152
3 145gr GC/BLL 2k fps BC ? Guess .266 Same profile as PB, Ogive & FP.
4) 145 PB PC CFE pistol 1400 fps BC ? Guess .266
Pulled the first 145 cast @ 100, went to top of target. Slower cast and HJ about the same @ 50, faster were about 1/2" diff from results @ 100; 2-1/2" vs 3" diff. My conclusion, BC doesn't make much difference < 100 yds. 100 yds, faster was at POA, slower were 3" low. At 50, slower were 1" high, faster 4" high (POA). then shot the bo pistol @ 50, the 145 PB PC. Still 'pushing' left a tad.