I did some interesting comparisons between chronographed velocities and formulas I picked up in ballistic books over the years.

.338 Win Mag : 250 GK bullet, charge decreased from 70.5 (clocked at 2743 ft") to 68.2 gn.
chrono : 2704 ft" � calculated : 2671 ft" = variance 1 %

.308 Win (7,62 Nato) : from 150 MK / 44.0 gn (clocked at 2805 ft") to 168 MK / 41.5.
chrono : 2546 ft" � calculated : 2549 ft" = variance .1 %

In both cases, the difference melts away within shot to shot variation.

Not bad for old timers formulas !

[ 07-24-2003, 13:51: Message edited by: Andr� Mertens ]

Andre':

Whose formulas, and what are they?

Andre',

But will the formulas give you the velocity if it is unknow? If the velocity is know can they give you the charge change required to hit a desired velocity?

It would be nice to run some numbers that will allow you to adjust your loads to get them where you want to be a little faster than add/subtract powder and re-chrono, several times .

You have to start with a known velocity. As a make do, you can use a manual but a starting chrono velocity taking your own variables into consideration (rifle, components, etc.)is the most accurate in my experience. I use 2 different calculations (to chek AND confirm the other) from different sources (one from Vihtavuori and I forgot where the other one came from). I've incorporated the formulae in a Excel form. If desired, I can e-mail it to parties interested so they can play with it and crosscheck my own findings (I will even push the courtesy and translate in English, ain't that courteous ).