FORMULA FOR RIFLE VELOCITY THAT WORKS;

VELOCITY EQUALS 8000 TIMES SQUARE
ROOT OF ALL OF FOLLOWING-----------
POWDER WT TIMES EXP/RATIO MULTIPLIER
DIVIDED BY BULLET WT & 1/3 POWDER WT.

VEL = 8000 X SQ ROOT OF ALL BELOW

_____________________________________
!.../
!../.POWDER WT X EXP/RATIO MULTIPLIER
!./_________________________________
!/
/.....BULLET WT + 1/3 POWDER WT



POWDER AND BULLET WT IN GRAINS.


THE 8000 CONSTANT IS FOR 45,000 PSI-
IMR POWDER.

USE 8300 FOR 50K IMR POWDER AND 45K
DOUBLE-BASE POWDER .

USE 8600 FOR 55K IMR POWDER AND 50 K
DOUBLE-BASE POWDER .

ADD 150 TO CONSTANT FOR CHAMBER SAME
DIAMETER AS BORE .


TO GET EXPANSION RATIO YOU TAKE TOTAL

VOLUME OF THE CHAMBER AND BARREL, AND

DIVIDE BY VOLUME OF THE CHAMBER .


HERE IS CHART OF THE EXPANSION RATIO EFFECT

WHICH SAVES A LOT OF COMPLICATED MATH,

MAKING ABOVE FORMULA EASIER. THE MULTIPLIER

IS ONE MINUS THE INVERSE OF THE 1/4 ROOT OF

THE EXPANSION RATIO.



EXPANSION RATIO.........MULTIPLIER

16 TO 1------------------.500

14.5 TO 1-----------------.488

13 TO 1-------------------.474

11.7 TO 1-------------------.460

10.5 TO 1--------------------.445

9.3 TO 1---------------------.430

8.3 TO 1----------------------.412

7.4 TO 1----------------------.394

6.5 TO I-----------------------.375

5.75 TO 1-----------------------.355

5.0 TO 1------------------------.333

FOR EXPANSION RATIOS BETWEEN THOSE ON
CHART YOU CAN INTERPOLATE TO GET MULTIPLIER.
THE FORMULA SHOULD BE WITHIN 2% FOR LOADS
AT OR ABOVE 90% LOAD DENSITY.
OF COURSE THERE ARE SLOW AND FAST BARRELS.
THE FORMULA DEPICTION I USED IS BEST I
COULD GET ON HERE.ED

Bumping this up for Lar45 and others.
This formula should be close to
within 4% for loads between 30,000 to 40,000 psi.
The constant you multiply in the formula will
be reduced for less than 90% loads.Don't use
ball for less than 90% loads.

Constant-
8600 is for 55k Imr powder & 50k for ball powder
8300 is for 50k Imr powder & 45k for ball powder.
8000 is for 45k IMR powder & 40k for ball powder.
7800 is for 40k Imr powder
7600 is for 35k Imr powder.
7400 is for 30k Imr powder.

Ed.

ahh.... of course its all clear now

Bakes

Thank you very much, I'll program that into my Calculator.

Bakes--The original military developed formulas
were a whole page.In this version we use what
is called a fudge factor, of assigning a constant
for different pressures and bullet jacket hardness.This system assumes a copper jacket bullet, and by assigning a constant for different pressures,and figuring out an expansion ratio
constant, eliminated 4/5 of the math used originally.For a hard jacket or full solid you subtract 300 to 600
from the constant depending on how hard it is.
And you have to get that figure by testing the
different hard bullets.IE use what reloading has shown the different brands of hard bullets doing.
And formula really makes wildcatting easier in
big bores, where folks may have uncertainty using
large powder amounts.Happy wildcatting..Ed.

Ed, one more question. Will this work for short barreled pistols also?? Is that taken care of in the expansion ratio?? What about for lower pressures down around 14k??

I guess that was more than one.

Lar--On most of the short barrel and low pressure
loads I have tried it on it don't correlate to the chrono.The expansion ratio part of the formula would have
to be on a fifth root of expansion and the type of fast powders used would make a real complicated math situation.Ed.

Sorry Ed you've still lost me...but then I get confused with the shopping bill

Bakes

Bakes, do you have access to MicroSoft Excel? If you do I can email you Ed's formula in a spread sheet. You would only have to fill in the shaded fields to get your answers.

Axel

Thanks, I've got it plugged into my TI-86, it seems to work fine. Is there a mathmatical conversion from the Constant to pressure? maybe I'll just try to curve fit it??

The mathematical relationship for the pressure constant (C) is:

C = 0.06*PRESSURE + 5300.

I am impressed at how accurately Ed's equation is to my store bought software and to reloading manuals.

Axel

That's probably because ED knows what he's talking about!-Rob

I have my own formula for computing velocity:

Velocity = whatever the reloading manual
says it should.

I also have an alternative formula:

Velocity = whatever the Shooting Chrony
says on that little LCD display.

That's about the limit of my mathmatical skills.

Rob- Axel- Thanks. It was only me knowing how to
use 60 dollar multiple root slide rule 45 years
ago that helped me figure this out.That was big
math tool then, IE no computers.And after years of reloading ball powders in comparison to stick, about 10 years ago I figured
for 90% plus loads of most ball powders that;
(.065 x pressure) + 5300 makes a good constant for them.The reason to simplify the constant, is
to be able to figure it for all the constants in
the general range you think the pressures will be,with simple math, and then when you chronograph, the one matching, tells you your pressure very close.(Most pyros have chronos,
very few have pressure equipment).A good safety feature in developing wildcats.And setting loads for cartridge longevity..Ed.

Axel
No offence to Ed (who's smart enough to understand this stuff!)I not really that interested. My first post was just my Aussie sense of humor. My formula for computing velocity is the same as GAHUNTER

Bakes

Bakes--You and GAHunter are doing it the right
way for reloaders and cartridge development-- IE; use that chrono.The best safety tool there is.Formulas are good for developement; but chronos are an absolute must.I have pyros loading
Weatherby stuff telling me how great their loads
are, and when you figure it out the loads don't do what they think. I have other pyros loading stuff that they think is ok, and they are way too hot,after they check them on my chrono...You know
""the book load didn't fill the case, so we filled it up"" syndrome.Ed.

I had the linear aproximation plugged into my calculator, but from the numbers provided, it isn't exactly linear. Looks like it might need an x^2. I have a chrony, but was mostly interested in a guess on pressure from chrono data. I plugged in some numbers from my Hodgdons manual and they all came up real close.
Thanks again.

I have a slide rule on my watch, but don't really know how to use it.