Hasty powder measure and approximation of capacity in grains by volume

[bgf]

I wanted something handier than the adjustable bench measure for a woods walk and had no time to find and get the right sized one online, so I made this powder measure from copper tubing and cross-pinned oversized dowel plug roughly shaped and then drilled to hang it:

It may not be pretty or HC, but it works great and is lighter than the standard brass ones.  Cost was as close to zero as you can get.  I can't imagine something similar hasn't been done many times in the past, and I actually like the way it looks in context .

The main reason, however, that I wanted to post this is that I found very little information handy on determining approximate size for a measure, and what I did find was not completely satisfying.

What I believe to be a straightforward and close approximation is this:

Capacity in grains = (Pipe_ID/2)² * pi * Pipe_Length * 248.047
where:
Pipe_ID is inside diameter of pipe (or cavity) in inches
pi = 3.14159...
Pipe_Length is unobstructed length inside pipe (or cavity) in inches

You can also start with the capacity desired and ID of cavity and determine the length necessary by rearranging things.  

Pipe_Length = Capacity_in_Grains/((Pipe_ID/2)² * pi * 248.047)

I couldn't seem to find a conversion factor for cubic inches to grains, except implicitly in one place where it seemed to be off by an order of magnitude when compared to measurements of chargers that I have.  In that case, the formula seemed somewhat over-complicated in my opinion as well, so I simplified it to the above form.  

Note that I realize the volumetric measurement of grains (a measure of weight) is approximate anyway, which explains to my satisfaction why the conversion is difficult to find. This is, therefore, a "rule of thumb" more than anything.  Obviously, verify the capacity with a known good measure before use: Using larger diameter pipe, especially, the capacity can go up pretty quickly with relatively small changes in length.   If anyone finds this formula in error or has a better, more exact, or otherwise preferable version, please correct me.  Otherwise, I hope it will be useful as a guide or starting point.

[smokinbuck]

BGF,
I've made a few measures that are similarly "primitive". I usually make the tube lomger than will be needed and then fill it to whatever charge I want from an adjustable measure. Once you find the level needed for your charge, mark the tube and cut it off. Formulas ?
Mark

[northmn]

If you get too technical it won't work anyway as even lots of the same powder can differ.  when I make a powder measure it is usually based on a commercial adjustable one.  BUT I often calibrate what the adjustable measure throws by weighing a couple of charges on a powder scale.  With 3f the commercial ones have been off by a couple of grains.  As stated, make one a little long and then cut it back and file it down. 

DP

[joelvca]

I couldn't seem to find a conversion factor for cubic inches to grains, except implicitly in one place where it seemed to be off by an order of magnitude when compared to measurements of chargers that I have.  In that case, the formula seemed somewhat over-complicated in my opinion as well, so I simplified it to the above form.  

What is the weight of a cubic inch of water?  The bulk densities I have seen for modern corned gunpowder have been fairly close to that of water.  If as certain Mad Monk happens to see this thread, perhaps he might be able to contribute some of his data.

Regards,
Joel

[bgf]

smokinbuck, northmn,
My thought was it would be nice to know approximately how long/deep the cavity needs to be, especially if your measure needs to be made with smaller or larger diameter pipe or drill than what you have on hand for comparison, e.g., you want to use small tubing for a .25 so the measure will go into the bore.  I don't think the math is much, if any, past grade school level, so I don't see how it complicates things; it is an option that need not be used if not desired.  I apologize if I'm not grasping the obvious.

joelvca,
That is a good approach (weight of cubic inch of water).  I ran across that in reading up on things, but I haven't pursued it, yet.  I would appreciate any correction or further refinement (e.g., FFG v. FFFG).

[Old Ford2]

I like your measure!
Old Ford

[bgf]

Old Ford,
Thanks.  I like to start out with stuff that doesn't need to be kept looking pretty, and that happens to be where my skills sets are:).

Joelvca,
If density of powder were exactly equal to water, the conversion factor would be 252 grains/in³.  Water weighs 0.0360 lbs./in³ and there are 7000 grains per lb, so the original value is a little more conservative. 

[sonny]

i like it!...don't know if early f&I period or colonials had copper pipes for measure.but i guess if they could make a copper pot some smitthy would do one for ya.........The adjustable measures! you know the pretty one's,never an i mean never through the same charge twice...I have found if the pipe,horn,cane or whatever you are using is just able to fit the tip of the powder horn,you get very close readings.If the measure is wide mouth so it could be made shorter,you will never,ever,get the same amount of powder.If you shake the powder horn or tap the measure you can really muddie up the charge numbers.........see what i learned???.....sonny-

[skillman]

Nobody has mentioned using wax in the bottom of the measure to get the right charge. This is a bit of bother but it lets you change the charge if you want.
Steve

[bgf]

Sonny,
Thanks.  I agree about the copper pipe being anachronistic, although no worse than lathe-turned  and extruded brass ones in my mind.  It would not be a bad way to make one using rolled brass or iron sheet with the wood plug, though, I think. 

S.Skillman,
Thanks for bringing that up.  I should have mentioned that I "fine-tuned" it by dripping wax from a candle into the bottom.  Its a really easy way to "adjust" the volume a little bit at a time when you get close, although you could fill it half way up with wax if needed.  The metal body comes in handy in this case, as you can heat the tube and get any dribbles off the side:).