Wednesday, February 17, 2010

Casting Lead Bullets

17 February 2010

First, a bit of background.

For a given distance from the center of the Earth, the attraction of gravity is virtually constant. If we use the surface of the sea as that distance, the force of gravity will be the same at Bombay, San Francisco or Narvik. There's some minor anomalies here & there -- there are a few crazy places on our planet where water actually does flow uphill -- but for all practical purposes we think of gravity as constant because it usually is.

If you raised a mass some distance above that surface then released it, it would take a certain amount of time to fall to earth. In fact, even if you threw the mass from you it would still fall to earth in the same amount of time, so long as your throw was perfectly horizontal. (If your throw happened to be slightly upwards then the object would take slightly longer to reach the earth.) Indeed, rather than simply dropping or throwing the object, let's say you hurled the object from you as fast as a speeding bullet or a rocket ship, the same rule applies: the object will take the same amount of time to reach the surface, the only difference being how far it travels before touching the ground.

I've mentioned this here because understanding the gravitational constant is fundamental to understanding the details of ballistics. The gravitational constant dictates the flight path of your bullet. To have the bullet fly straight to the bullseye, you want it to fly there as fast as possible, since the shorter the flight time, the less time gravity will have to influence the downward motion of the bullet. But the faster the bullet travels, the greater the chance it won't travel in a straight line. Aerodynamic forces will cause the bullet to tumble. Before we can take advantage of firing at a higher velocity we need to come up with some method of stabilizing our bullets. The way we do that is to spin the bullet, taking advantage of Newton's laws of motion, specifically,the fact that a body in motion will tend to remain in motion until something comes along and changes it. So how fast is our bullet spinning? And just how fast is it traveling down-range? I thought you'd never ask :-)

If we were talking about a muzzle-loader, it's rifling would be on the order of one turn every four feet or thereabouts, and it's muzzle velocity would be about a thousand feet per second. But if we were talking about a modern, post WWI rifle,the twist would be about one turn every ten inches and the muzzle velocity would be almost three times as fast as the muzzle loader, typically around 2700 feet per second.

One turn in four feet (for our muzzle loader) and an initial velocity of 1000 fps means out bullet -- in this case a lead ball -- is spinning 250 times per second as it leaves the muzzle. That's fifteen thousand rpm. More would be better but even 15,000 rpm is pushing it when dealing with a lead projectile because lead simply isn't very strong. Try to spin it any faster and it will simply shear-off where the lead engages the lands of the rifling. A modern weapon, with a rate of about one turn in every ten inches (0.83 feet) and a muzzle velocity of 2700 feet per second has our modern copper jacketed bullet spinning nearly 200,000 rpm. Now we're talking some serious spin -- and a superbly stable projectile.

With a spin-stabilized bullet, a modern firearm is capable of putting ten shots through the same hole in a target a mile away. But that brand of accuracy is very expensive, with each shot costing several dollars.

The more we practice our shooting... the more bullets we fire... the more accurate we will become. On average, the difference between a marksman and a Life Master is about 250 bullets per week. That is, if it takes you fifty practice shots per day to become ...and maintain... your skill as a marksman, doubling that amount of practice will turn you into a Life Master... an Expert Marksman. The problem here is the cost.

By reloading our own bullets we can reduce the cost per shot from over a dollar per shot to something significantly less, the exact amount depending on the price of the primer and powder. We will re-use the brass cartridge case and cast our own bullets. Even so, the lead needed for the bullets reflects significant cost, so what we'll do is begin with used wheel weights.

A wheel weight, as used for balancing tires, is typicaly 95% to 97% lead. Tin and antimony are used to harden the lead but it is the lead that is crucial here. The velocity of our bullet is a function of its mass and the power of the explosive charge that drives it from the barrel. Once the bullet is free of the barrel, the shape of the bullet has considerable effect but right now we're only interested in what is known as interior ballistics -- the stuff that happens before the bullet leaves the barrel. (Once the bullet flys free, it's characteristics are referred to as exterior ballistics.)

The nice thing about old wheel weights is that they are inexpensive. Indeed, many gas stations and tire shops don't bother to recycle them and may even give them away. But for most of us, paying two-bits a pound is more the norm.

We need to know the weight (or mass) of our cast bullets in order to select a suitable powder charge. This is one of those cases where no guessing is allowed, since an error can result in a damaged firearm or even worse, a damaged gunner.

Once you have a batch of old wheel weights, typically five to ten pounds, you melt them down and cast them into ingots of known volume. By accurately weighing the ingot you can determine what percentage of their weight is not lead. You then re-melt the ingots, adding enough pure lead to correct the mass.

Melting lead or any of its alloys is fairly simple because it melts at such a low temperature -- pure lead melts at 621.5 F, which means you don't need much in the way of smelting equipment to turn wheel weights into ingots. Indeed, a few charcoal briquettes provides more than enough heat to melt ten pounds of lead, although a kitchen stove is more convenient and an electrically-powered smelting pot like the one shown in the photo is the most convenient of all.

Once the content of your lead has been adjusted the metal is typically re-cast into ingots of convenient size, typically of 1/2 lb, 1 lb and 2 pound weight. This makes for easy storage and casting.

I reload ammo for eleven different calibers, not including the balls I use in several black-powder firearms. The distinction here is that cartridges are usually not made up for black-powder weapons. Unlike modern smokeless powder that is virtually inert, chemically, black-powder can be extremely corrosive, making it unwise to pre-load it into cartridges or even into your firearms, until just prior to its being used. But modern smokeless powder can be used safely after twenty or more years.

The 'grain' is the usual unit of measure for the mass of a bullet and there are 7000 grains to a pound. The bullet for a small pistol may weigh less than 100 grains whereas a large slug for a blackpowder rifle might weigh more than 25ogr. The 9x18 Makarov uses a bullet weighing about 95 grains or about 73 bullets to a pound of wheel weights.


To cast a bullet we first need a bullet mold. If you are a machinist you can make your own molds but most most people -- including machinists -- prefer to buy their molds from dealers who offer reloading supplies. In the photos you will see some of the many molds I use. The sprue hole of the mold is pressed against the spout of the melting pot and the lever is raised, allowing molten lead to flow into the mold. You may cast as many as six bullets at a time although two is the most common number.

When the mold is filled you release the lever, allow a few moments for the lead to cool, then give the sprue-cutter a sharp rap with a wooden maul. Cutting off the sprue frees the bullet from any over-flow of lead,whilst opening the mold allows the bullet to drop free. The freshly cast bullets are then collected, ready to be coated with lubricant. The lubricated bullet are passed through a sizing die which swages them to a precise diameter, such as .357" for 38 Special, or .356" for 9mm Luger. But the 9x18 Makarov bullet is actually 9.22mm or about 0.363". To produce a bullet of the proper size it is customary to begin with a cast slug at least 0.365" in diameter; to lubricate the exterior and to then pass the cast slug through a set of swagging dies to produce a bullet of the desired diameter.


Saturday, February 13, 2010

A Very Good Day

Since being diagnosed with multiple myeloma good days have become rather rare around the Hoover household; rare enough so that when one occurs I often feel the need to share it... with today being a nice example.

I have guns all ovet the house and I wear one whenever doing so is not only practical but legal. But simply having a firearm is of little use if you are not qualified to use it. The only way I know to maintain your abilities with a firearm is use one. That means firing it frequenty; ideally, every day.

The pistol I'm wearing is a Makarov. It uses the 9x18 Makarov cartridge, which is NOT the same thing as the Short Lugar... which is ALSO 9x18. To develop and maintain my proficiency calls for burning a lot of powder. Unfortunately, Mak ammo is fairly expensive. Normally, I wouldn't pay much attention to the cost since I reload my own ammo, and while the 9x18Mak isn't commonly available, as a low velocity pistol round it's dead simple to reload. So that's what I've been doing but using LEAD bullets instead of better quality jacketed slugs.

Today I turned 10+ pounds of wheel-weights into 11+ pounds of lead alloy suitable for bullets. You can't use wheel-weights straight off because they contain a tad too much antimony and not quite enough lead. So you melt the wheel-weight into 1/2lb ingots then figure out how many #00 buckshot must be added to each half-pound. Melt that together and you've got a suitable alloy for Makarov pills.

Shells aren't a problem because regular 9mm brass, using Boxer-type primers, can be used in the Mak once the casing is trimmed to the proper length. This allows the use of Small Pistol primers and regular 9mm brass, which when combined with an accurately cast lead bullet, brings the cost of maintaining your proficiency within reason for even the most cash-strapped marksman.

The fact everything worked out okay is one of the reasons today was an especially good day. The other reasons have to do with a new refrigerator, in that our old refrigerator was too short for three people, the new number of residents at the Hoover household.

To install a larger refrigerator called for removing the cabinetry above the old refrigerator. Once it was removed we needed to shorten the existing cabinet. The main problem with doing so was the fact the kitchen has a dropped ceiling and the fact I can no longer raise my arms over my head. Fortunately, the new permanent resident is our daughter, who proved to be a Terror when handed a Skilsaw... or any other other tool of mass destruction.

How high was the needed adjustment? One half of an inch. How long have we worked on it? Several days. But today brought all the bits together so that all that remains is to put the new cabinet in place.

Finally, the best news -- and justification for any Special Day... it was just thirty-three years ago today that June Carol Yates became my bride. I love her still, as she does me.


Wednesday, February 3, 2010

Solved! - A Standard Engine for Homwbuilts

The final piece of the puzzle fell into place when DuraFix altered the alloy of their aluminum brazing rod. The new rod allows us to apply the Fat Fin modification without fear that the extended fins would crack

For those who have not followed the development of this engine, it' specs are as follows:

2332cc displacement (142cid). That is, a perfectly 'square' engine having a bore AND stroke of 84mm. Rod length is 142mm (5.6"). Compression ratio is 8.5:1.

( - 13 February 2010 -
My thanks to the several of you who caught this error. The 'square' engine would b 84 x 84... or perhaps 94x94... but it would NOT be 84x94. [My interpretation of the Standard Engine is one having a Bore of 94mm and a Stroke of 84mm.] So please accept my apology for this gross mis-statement of fact, for which I've no excuse... although I may be able to come up with one, given enough time :-)

The propeller is installed on the clutch-end of the crankshaft. You may fabricate the required spool & propeller hub yourself using the dimensioned drawings contained in the HVX Files or you may purchase them from Great Plains Aircraft Supply Co (GPASCo).

A 20A. alternator is installed coaxially on the pulley hub. The guts of the alternator are taken from a Harley-Davidson motorcycle. A kit of parts, including the required regulator, is available from GPASCo.

The engine conversion includes the HVX modifications. A swaging tool for installing the Toyota valve seals may be fabricated from the drawings or purchased from Mike Sample.

There are a wide variety of carburetors that will work with this engine. Least expensive is the Tillotson Model-X whereas most convenient is probably one offered by GPASCo.

The engine uses either single- or dual-port heads and may use either single or dual ignition. Unless dual ignition is required by local authorities, single ignition is recommended.

The lightest and least expensive ignition system is the stock Volkswagen system based on a mechanical-advance distributor (ie, the -009). This system uses regular ignition points which should be replaced every 100 hours. The system my be improved by eliminating the points using a solid-state points replacement module, or converted to a Waste Spark system using the CompuFire DIS-IX, although the latter is significantly heavier and about 4x more expensive.


The above defines the basic engine. Engines of other configurations will work but the key factor is overcoming the Volkswagens inherent thermal limitation as dictated by the fin-area of the cylinder heads. The 'Fat-Fin' modification provides an elegant solution to the thermal limitation by increasing the fin area.

-2 February 2010