Home Forums Hunting & Shooting Ask The Gunwriters weight of lead in grains by volume

Dr. Howell: In your reference library do have any information on the weight of lead by volume (grains/cubic inch or ounces/cubic inch being much preferable to grams /cubic centimeter)? There's a limit to how many conversions I am likely to get correct in any one day. <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />
I would like to calculate how much weight I could gain in a bullet by altering its length a certain amount and ultimately get a mold made to do it.
Many thanks.

Pure lead weighs (nominally) 0.4096 pound per cubic inch. That's 0.4096 � 7,000 = 2,867.2 grains.

But your bullets -- cast or jacketed -- aren't all lead, so the workable weight per cubic inch is something less -- and I can't guess how much less. There's an equation for finding the weight of an alloy or heterogeneous bullet relative to the weight of the same volume of water -- by weighing the bullet suspended (by an essentially weightless thread or wire) in the air, then in water. Some of the better scales used to have a double hook on the beam and a beaker platform on the base for making these two weight measurements.

But I haven't seen that equation in decades, don't remember it, and don't know where to find it or how to derive it. I'm sure that some of the better educated guys here can supply or derive it and will post it here. (I hope so -- I've wanted to recover that equation, for lo! these many years!) If I find it, I'll post it. It may be more dependable than hardness for comparing cast-bullet alloys for their relative consistency.

Well, FWIW, I think I've fingered it out. I'll give my reasoning, and somebody can check it for us.

Old Archimedes first figured-out that an object in a liquid is buoyed-up, supported, or "lightened" by a force equal to the weight of the liquid that it displaces. A bullet suspended in water, therefore, must weigh its weight in air minus the weight of the water that it displaces. Its relative density -- its weight in air divided by the weight of the water it displaces -- is therefore its weight in air divided by the difference in its two test weights.

If I'm right, then the "lost" equation is

x = a/(a-b)

if
a = weight of the bullet suspended in air
b = weight of the bullet suspended in water
x = specific gravity

The weight of the bullet per cubic inch, then, is the weight of a cubic inch of water (about 0.0361 lb or about 252 to 253 grains) times the bullet's specific gravity as determined above.

But at this time of the night, after a day like today, I'm not the first bit certain that I've figgered this right. <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />

Dr. Howell:

The weight in grains per cubic inch is close enough for my purposes. If I really want to fine tune it I'll cast a bullet in pure lead and compare it to the weight of a bullet from my usual bullet metal and come up with a percentage which should also apply to the volume of the projected increase. For what I have in mind an increase in volume of.006 cubic inches of volume would add 17.2 grains of weight to the bullet. In practice it would be slightly less than that (unless I use that extra metal to produce a two-part soft nose bullet).
Thank you for digging that out.

On rechecking my volume calculations I found I had erred. Weight increase will actually be closer to 40 grains which is significant (348 Win). Now to play around with some bullets and a file and see how much meplat will actually feed smoothly through my 71. Ultimately hope to order another mold from Mountain Molds that will cast at 250 grains or a bit higher.

You need AutoCAD.

Several years ago, a bullet company hired me to redesign the classic round-nose .38 Special bullet so popular with cowboy shooters, to give it a meplat wide enough to span primers (in tubular carbine magazines), yet maintain the original weight. In AutoCAD, I drew the bullet and got its volume. Then I drew it with the meplat and got its smaller volume. Finally, I drew it with a wider bearing band just forward of the crimping groove until I got the volume back up to the original volume.

After the moulds were in production and use, I asked the manufacturer and was told that indeed the redesigned flat-nose bullets cast to exactly the same weight as the unaltered original round-nose bullets. You'd find redesigning to an exact lighter weight dog-simple with AutoCAD. Trouble is, AutoCAD ain't cheap. (Neither was I -- got $600 for that job.)

Dr. Howell,

Some articles just leave an impression on us. This was one sticks in my memory.
I believe the article you are thinking of is: "The Lead Content of Cast Bullet Alloys" by Frederick A. Hohorst. This was in Handloader #75, page 24. It was also reprinted in The Art of Bullet Casting (Wolfe - you knew that!) page 94. The last page has the formula, the first page the pictures.

I am new to this forum and have been looking for a discussion of cartridge efficiency. Your formula is a good one but has raised a few questions....