a little math help.

[fiver]

I know how to figure out the bore volume on a rifle barrel or whatever.
but I don't know if there is a formula [or a BTU figure] to calculate the gas volume from a volume of gun powder.
I would imagine the burn rate is about meaningless without a projectile on top of it.
but I would like to be able to calculate or close enough calculate a volume of gas available in some loads.

 

[Brad]

Answer



My head

 

[KeithB]

I imagine there is probably both theoretical and measurable ways to calculate gas volume. You would probably get something based on STP (standard temperature and pressure) which could be used to compare different powders. I think every powder would have a unique figure associated with the volume generated per grain of powder. How well that could be used is open to discussion. We know some powders have a reputation of burning hot, or incompletely, and of course the only time the gas volume will see 15 psi and 78 degrees is AFTER it has left the barrel.

 

[RicinYakima]

It is totally dependent upon composition of the powder, plus additives. All IMR DuPont powders have the exact same chemistry (why Hutton could make his slide rules for estimating pressure and conversely loading data), but not all. Hercules, now Alliant, now who ever has the cheapest manufacturing facility, varies the amount of nitroglycerin in the formula, so not useable. WW or Olin uses so much deterrent and coatings, it is anyone's guess per lot number. I'm afraid you are on a hunt for information that will change with every lot number of powder you buy. Sorry, Ric

 

[Ian]

It's called "Quickload" by Neconos. They use a formula based on the heat of explosion, burning rate factor, some factors that establish the time of rise to peak pressure and fall (pro- and di-gressive burn rates), and some other stuff for each powder. After that, it's just plug-and-chug to get the energy formula for the powder in a given system once you input all the other pertinent stuff about the system. The final formula probably boils down to a simple second derivative, but you'll never pry it out of them. I realize your money tree froze to death last winter, but QL is the best $160 I ever spent on this hobby.

 

[RicinYakima]

Provided that the lot of powder you have is close to the one worked up by the German fellow who wrote "Quickload" almost 20 years ago now. Ian is correct in that it is within 5% of almost all powders, but also, like he says, you have to use wise judgement! I have used it, and it works. But for what you are asking, I don't know that there is a gas volume answer.

 

[fiver]

i'll get beck to this a bit later today.

 

[Ian]

I'd offer to run some examples for you if it would help, but if you're messing with shotguns the program is no help (unless I've missed something, which is entirely possible).

 

[fiver]

no I got the shotgun thing figured out.
even oversized hulls and long wads ain't much of a challenge to predict pressure changes anymore,
and figuring the gas volume for them wouldn't be helpful really, they pretty much run out of gas by the end of the mouth of the hull.

I just got to thinking about pressure testing in the old day's and just how the mag writers had a clue as to what was 'over bore' and what wasn't.
I thought I had seen some type of calculation somewhere [probably for expanding solid nitrogen or CO-2 into a gas]

anyway.
we have an absolute pressure 'limit' right?
we know staying at the pressure limit for as long as possible produces the highest velocity.
we also know a longer barrel can give higher velocity's.
I have done enough pressure cap testing [where I pick a pressure of say 19,000 psi. then work loads with different powder speeds and observe the velocity/accuracy change etc..]

I just was thinking if I could figure a gas volume for a powder volume of flake powder, one for ball powder,and one for stick powders I could use them to better narrow in a barrel bore volume prediction without going over.

 

[RicinYakima]

What you want is available from the "Powley computer for handloaders" ( a slide rule) with the "Speer ballistics calculator". However neither have been sold since the early 1970's and only work with DuPont IMR powders.

"we have an absolute pressure 'limit' right?
we know staying at the pressure limit for as long as possible produces the highest velocity.
we also know a longer barrel can give higher velocity's.
I have done enough pressure cap testing [where I pick a pressure of say 19,000 psi. then work loads with different powder speeds and observe the velocity/accuracy change etc..]"

What you want is a program to calculate the total area under a curve. If you can get the curve from "Quickload" there are programs on the net to do the calculation. Or if your calculus is up to speed, you can do it with paper and pencil.

HTH, Ric