[Southpaw]

Does anyone out there know the math formulas used for Thorniley Stopping Power, foot pounds of energy, or Recoil?  I know the calculations are available through the Ballistician's Corner, but I'm building a spreadsheet to programmatically compare different bullets, calibers, etc. using several formulas.  I'm missing these formulas.  I thought it might be handy in evaluating different guns and/or loads for particular situations.  Thanks in advance.

 

[Bill Lester]

The only one you asked about that I can help with is the formula to determine energy in foot/pounds.

Velocity Squared (in fps) X Bullet Weight (in grains)
                              450,400

Another formula you may find useful is the one to figure
Sectional Density.

SD=Bullet Weight (in pounds)
       Square of the Diameter

Remember that there are 7000 grains to the pound and you should have no trouble.

 

[Jack Monteith]

Hi, Southpaw:
    General Hatcher's recoil formula is:

((Bullet wt.*velocity)+(4700 * powder wt.))/(7000 * gun wt.)
= recoil velocity

1/2 ( recoil velocity ^2 x gun wt.)/32.16 = recoil energy
 
  Given General Hatcher's 8.69 lb. Springfield firing a 150 grain bullet at 2700 fps with 50 gr. powder:

V = ((150*2700)+(4700*50))/(7000*8.69) = 10.52 f.p.s.

E = 1/2 * 8.69 * 10.52 * 10.52 / 32.16 = 14.95 foot pounds

  The constant of 4700 is the powder gas velocity. It's probably too low for the barrel burners and too high for large bore cartridges like the .45-70. I've seen a constant of 2000 used for black powder.  Needless to say, I don't have the equipment to measure gas velocity out here on the farm.

  Bill uses the constant of 450400 in his energy formula.
450400 = 2 * 7000 * 32.17142+.  32.17 foot per second per second is the currently accepted value for the acceleration of gravity, but older references like General Hatcher's Notebook use 32.16 for a constant of 450240. This explains why some energy numbers differ slightly.

  Hope you can figure this out.  

Bye
Jack

 

[Southpaw]

Bill, Jack...Thanks a lot!  I forgot about sectional density.  I did want that for sure.  I've got everything working, but one thing was interesting.  I had to drop from 4700 to 2500 in calculating the velocity to get the same results as on the Ballistics Corner.  I checked several  of my results with the Ballistics Corner for verification.  This is what I have so far for calculations: sectional density, energy, recoil energy, recoil velocity, penetration and cavitation. The last two are based on an article posted by someone in one of our forums, but I can't find it right now.  It's a thread that Marshall started, but I can't find it right now. I find all this interesting because now I can evaluate the relative effectivness of a load/gun combination and its associated recoil.  I use a a baseline a gun/load that I have fired... in this case a 44M RH using Garrett Cartridges 330gr LBT cast @ 1385fps.  If you have any other suggestions, I'd appreciate it.  Also, this is a just Microsoft Excel spreadsheet, so if it's useful to you or anyone else, I think I can E-Mail it.  I can try anyway.  Again, both of you, thanks a lot.