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| Prices | Specials | How To | Bullets | B.Makers | Books | Classified | |
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The following is a chart of production output for a given material input (that is, how many bullets or jackets you can make with a certain number of pounds of copper strip, lead wire, etc.). Naturally, there are variables in the design of bullets that require certain general assumptions, so that you may actually make a few more or less from the same material depending on the specific bullet. But in general this is a reliable planning guide for matching jacket and core material purchases, and calculating your production costs. For a discussion of how to determine production speed, see Production Speed page. To find the current cost of copper, jackets, lead wire, and other supplies, see the Price List page. |
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CU30-625 50-lb coil |
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CU30-100 50-lb coil |
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CU30-125 50-lb coil |
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CU50-125 50-lb coil |
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CU94-140 50-lb coil |
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Assumptions: You will use Corbin's deep-drawing grade ASTM C11000 copper to draw the jackets. The density of the copper is 0.325-lb/cu-in.
The copper is sold in "pancake" or flat coils of 50-lb weight, in standard width/thickness dimensions as follows:
Calculation Methods The product of jacket wall thickness, caliber, and length determines the volume of material in the finished jacket. This volume must be the same or less than the volume in the original disk from which the jacket is drawn. Therefore, any jacket can be made longer if it is thinner walled or smaller diameter, thicker walled if it is made shorter or smaller diameter, and larger caliber if it is made with thinner walls or shorter length. The number of jackets per a given weight of copper strip depends on the width and thickness of the strip. Copper strip is sized to provide the least amount of scrap for each jacket drawn, and is therefore matched as well as standard inventory allows to the desired jacket parameters. The jacket material is used to punch a disk, which must allow for a small buffer space between the edge of the strip and the start of the disk. The assumption is that this buffer will be 0.015-inches on each side of the disk. Therefore, subtract 0.015 x 2 = .030 inches from the width of the strip, and this will be the maximum disk diameter. (The actual buffer may vary somewhat, but for calculation purposes .015-inches is reasonable.) Therefore, a 0.625 wide strip (5/8-in) can make a disk of 0.625-.030 = .595 inches diameter (maximum). The number of these disks that can be cut from a 50-lb coil is the length of the strip in that coil, in inches, divided by the width of strip. The number of inches of length of any weight of coiled strip is determined by dividing the volume by the strip width times thickness. The volume is determined by the weight divided by the density. (Density is weight divided by volume). The density of Corbins material is 0.325-lbs/cubic inch. Therefore, 50 lbs divided by 0.325 lb/cubic inch is 153.846 cubic inches. This is the volume of ANY 50-lb coil, regardless of the width and thickness, so long as it is the same density. To determine the length in inches of any coil, calculate the square inches of cross sectional area for the strip, and divide this into the volume. The cross sectional area is the width times the thickness. Here are the cross sectional areas for standard Corbin copper coils:
To calculate the scrap weight for recovery (sale of scrap copper), simply subtract the area of each disk from the area of the square (strip width squared) from which it is punched, and subtract the disk area from the square area. Multiply this remaining area by thickness, to obtain volume. Multiply the volume times the density of copper for the weight. You can then call a local scrap metal recovery firm, and ask what the current purchase rate may be for pure copper, by the pound. Multiply this dollar value by the scrap weight, subtract from your material cost, and you have the net price of the jackets.
To break this down in simple terms...
For any strip width, the number of jackets you can make in any weight of material is simply the length of that coil divided by the width. Normally, you don't know the length but you do know the weight, width, and thickness. Here is how to calculate the length and number of jackets you can make:
A = Width * Thickness |
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Calculating your cost per bullet for lead cores is straight-forward. There are 7,000 grains in a pound. A 10-lb spool of lead wire contains 70,000 grains. Your bullet weight is the combination of core weight and jacket weight (if a jacket is used). Therefore, simply subtract the estimated jacket weight from the bullet weight, and divide the remaining core weight into 70,000 to find out how many bullets you can make with one spool of wire.
Jacket weight is not always known in advance, but you can estimate closely enough for reasonable calculations. A normal 224 jacket (which means, about 0.705-in long, and works for all the 5.7, 5.65mm, .223, .220, .225, etc. calibers) weighs about 15 grains. A .243 or .257 jacket can push that to 20-25 grains. A typical 30 caliber bullet will be around 30-40 grains. Longer and heavier wall jackets in a given diameter weigh more than shorter, thinner jackets, of course. But a general estimate is usually close enough to be useful. Later you can actually weigh the jacket you plan to use, and recalculate based on whatever it may be. A carton of four spools weighs 280,000 grains. If you are making 180 grain .308 bullets, and the jackets weigh about 40 grains, then each bullet uses 140 grains of lead. Divide 280,000 by 140 and you will find that you can make 2,000 bullets with a carton of lead wire. That means you should order 8 bags of .308 jackets (250 per bag) for each carton of lead wire. If you were making 55 grain 224 bullets, and the jackets weighed 12 grains (rimfire case jackets, perhaps), then the core weight per jacket would be 55 - 12 = 43 grains. Dividing 280,000 grains in a 4-spool carton by 43 = 6,511 bullet cores. So you would want to make that number of jackets to match the core supply. You can see how easy it is to calculate how much lead wire you need to make any given weight and quantity of bullet. |
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To determine material cost for a given bullet, calculate the core weight you plan to use. If you are making a 450 grain .458 rifle bullet, for instance, and the jacket you are making from copper tubing weighs about 70 grains, then the core weight will be 450 - 70 = 380 grains. Divide this 380 grains into 70,000 grains for a spool of wire. The answer is 184 (always ignore fractions when calculating the bullet quantity from weight).
Now, divide the cost of a spool of wire by 184. This is the core cost per bullet. The jacket cost is either what you pay for a package divided by the quantity in the package, or it is the cost of the tubing or strip divided by the quantity of jackets you can make from that amount of material. With copper tubing, the number of jackets per foot of tubing is the length of the jacket plus half the caliber plus the saw cut width divided into 12. Most of the time, you can estimate that a jacket will be about an inch long, for typical bullet weights in the medium and larger bores (not huge bores like .510, of course, and not for extreme high BC, extra long or heavy bullets). So add half the caliber to 1, and add about .030 more for the saw cut. In a .458, this would mean each bullet uses 1.0 + 0.229 + .030 or 1.259 inches of tubing. To be on the safe side, round this up to 1.3 inches per bullet. Then if you purchase, say, 50 feet of tubing total, you know this is 50 x 12 or 600 inches, and divided by 1.3 per bullet makes 461 bullets. If you paid $150 for the tubing (only as a math example: this is NOT the actual price at any given time), then divide 150 by 461 and your jacket cost is 32.538 cents. Add to this your cost of lead, and you will know what the materials cost. |
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