Weight is Volume?
Never knew people used "Grains" to mean either weight or volume . . . sounds like a good "weigh" to confuse things!
I used density = weight (grains)/volume (in^3) which I believe is a pretty good working definition.
Started with baseline data developed experimentally - guess I have to trust the guy who reported this on his website (
http://www.tbullock.com/bpsg.html):
********excerpt from website***********
Powder Density I made a cylindrical powder measure with a depth of 1.000 inch, a diameter of 1.128 inches, and a volume of one cubic inch. I measured and weighed all the powders I could get ahold of, and measured some power dippers.
Density of Black Powder
Powder Size Grains per
cubic inch Notes
GOEX Fg 235
GOEX FFg 231
GOEX Ctg 252 Surprisingly Dense
GOEX FFFg 238
GOEX FFFFg 235
Dupont
Superfine FFFFg 232 70 years old and good as new
Dupont
Superfine FFFg 243
Kik FFg 230
242 Antique powder dipper
248 1970's T/C powder measure
Average 239
Quite a variation. That is why you measure powder by weight and not by volume. The average seems high to me; 235 is the value that I would likely use when making a powder measure.
********end excerpt from website***********
The volume of my patent chamber was estimated from a variety of cylinders using "go-no go" for diameter and depth of penetration. Couple of assumptions made (assumption of cylindrical shape, for one) but pretty sure my measurement is at least accurate, if imprecise.
Then calculated the volume using our old friend 3.14159 and pi*r^2*l to get volume of patent chamber.
Took density of black powder from table (above; used 238 gr/in^3) and multiplied by volume of patent chamber (cubic inches cancel out) to get grains in weight of the black powder.
I'm pretty sure I did all that right . . . I didn't realize that density or volume had different interpretations (but that mass vs. weight thing always gave me pause!).
Steve in North Texas