How to use ballistic program with cast bullets

[elginrunner]

I've been using a ballistic programs since the 90's (barnes on 3.5" disk), to pointblank (freeware), to ballistic (on iphone). Much to my chagrine I discovered that only j-word projectiles are available on the ballistic program. However it looks like raw numbers can be entered into fields...

A program of this type will come in handy shooting my 375H&H with cast, but what drag model to use for a flat nose 250 grain?? Where do I find the B.C.??

Any thoughts or experiences?

[kir_kenix]

BC is fairly easy to figure out (or approximate) with a known velocity, boolit weight, with a known set of conditions (temp, wind, elevation, baryonic pressure, and relative humidity), and compiled dope (drop at known distance). I use a BC calculator that approximates a given BC in those conditions. My calculator is run on MATLAB, but I am sure there are a ton of various ones that could be found on the web for free.

I even run the numbers with jacketed bullets (bullet mfg's lie!...some people only look at these numbers after all...) to better approximate drop at longer ranges. I've found that virtually all of the bullet mfg's BC claims are overly optimistic (Nosler is pretty close, and Barnes is decent). Norma and Hornady seem to be the worst offenders of overhyping BC from what numbers I have crunched.

[kir_kenix]

Forgot to add...when I said boolit weight, what you really need to know is the SD (sectional density). Remember that we use BC as a constant in most ways, but it really isn't one. It is just a comparison to a reference bullet and formula derived by some French guy came up with. It works really well for what we use it for, but it is far from perfect. While we use BC mostly to approximate drop over distance, it is actually a lot more useful to determine Kinetic energy retention at a given distance.

[Norbrat]

Try this: http://tmtpages.com/calcbc/calcbc.htm

[10x]

Hatcher's Notebook has a section on ballistics - and most of the formulae you will need. The lyman cast bullet handbook (3rd Ed) has a formula to calculate bullet drop using a rifle scope or iron sights.
A long time ago - 1985, I wrote a ballistics program in basic.

What I learned about B.C. (ballistic coefficient) is that it changes as the velocity of the bullet changes. B.C. is a comparison to a standard bullet fired at a know velocity. A bullet with B.C. of one will duplicate the trajectory of the standard bullet.
As the bullet drops to the speed of sound and below the speed of sound the ballistic coefficient can change dramatically. Below the speed of sound a pointy bullet ( with a boat tail) is going to retain velocity for a longer distance than a Flat point , plain base bullet.

The following is a very simple basic program to calculate drop and wind shift
(From an old gun magazine)

10 ' SIMPLE BALLISTICS
20 ' SAVE AS BARNETT.BAL
100 CLS:LOCATE 10,30:PRINT "BALLISTICS BY BARNETT"
110 FOR N= 1 TO 500: NEXT N:CLS
120 LOCATE 7,25:INPUT"ENTER MUZZLE VELOCITY ";A
130 LOCATE 9,25:INPUT "ENTER BALLISTIC CO. ";B
140 D=.0001143/B
150 IF A<2600 THEN D=.0001257/B
160 LOCATE 11,25:INPUT "BULLET WEIGHT IN GRAINS ";C
170 LOCATE 13,25:INPUT "SCOPE HEIGHT IN INCHES ";E
190 LOCATE 15,25:INPUT "ZERO RANGE IN YARDS ";F
200 LOCATE 17,25:INPUT "ELEVATION ANGLE IN DEGREES ";R
210 G=96.48001/(D*D*A*A)
220 H=(G*(EXP(6*D*F)-1-6*D*F)+E)/(36*F)
230 LOCATE 19,25:INPUT "RANGE DATA REQUIRED ";I
240 J=3*D*I:K=(EXP(J)-1)/(D*A)
250 K=INT(1000*K)/1000
260 BEEP
270 CLS:LOCATE 7,25:PRINT "TIME OF FLIGHT TO X ";K;" seconds"
280 L=INT(A/EXP(J))
290 BEEP
300 LOCATE 9,25:PRINT"VELOCITY AT X IS ";L;" f.p.s."
310 M=36*I*H-G*(EXP(2*J)-1-2*J)*COS(R)-E
320 M=INT(M*100)/100
330 LOCATE 11,25:PRINT "DROP AT RANGE X IS ";M;" inches
340 N=INT(C*L*L/450240!)
350 LOCATE 13,25:PRINT "ENERGY AT RANGE X IS ";N;" ft. lbs."
360 O=17.6*(K-3*I/A)
370 O=INT(100*O)/100
380 LOCATE 15,25:PRINT "WIND DRIFT AT RANGE X IS ";O;" inches for 1 m.p.h. crosswind"
390 LOCATE 17,25:PRINT"CALCULATE ANOTHER ONE, Y OR N "
400 A$=INKEY$:IF A$="" THEN 400
410 IF A$="y" OR A$="Y" THEN 120
420 END

[kir_kenix]

As Norbrat posted...looks like a good calculator. Looks like it even calculates for GL, G6, and G8 drag curve models in cast boolits. I could have quoted the wrong BC models...but it looks like this calculator will do everything you will need it to do in a .375 H&H. I think that Lupua, Norma, and Berger (??) use Doppler radar to calculate BC...and stay away from curve models and interpolation as much as possible.

Remember, you a comparing your boolit to a standard, and your BC is really just a comparison to that standard. Just happens this is good 'nuff for what we do.

[Harter66]

I use nobrat's link and a Strelok calculator app it works well out 400 yds w/my PP'd 7mm matching the table numbers.

[Von Gruff]

I use the RCBS BC guide as a starting point and for my purposes it sufices. I am not trying to get to 1000yds with my cast loads as 200-250 is max with what I shoot.
RCBS Cast Rifle Bullet Ballistic Coefficients
22-055 FN .159
243-095 .258
257-120 .272
270-150 .327
7mm-145 Silh. .272
7mm-168 SP .306
30-115 SP .175
30-150 FN .220
308-165 Silh. .286
30-180 SP .293
30-180 FN .255
35-200 FN .243
357-180 Silh .210
375-200 FN .220
44-200 FN .130
429-240 Silh .186
45-300 FN .207
45-405 FN .303
45-500 FN .365