An Easier Way to Cast Good Bullets

NRA Cast Bullets Supplement No. 1 March 1990 page 15 [page 17 physical]

A bullet mold, to reloaders who just want to cast bullets of reasonable quality, is simply a mold. On the other hand, there are some reloaders who want a perfect product, who are seeking tighter groups, higher scores, and more satislaction than is provided by simply hitting a can or keeping them all in the black. I belong in the latter group.

On top of the list of highly valued qualities which all bullet molds should have is the ability to cast a perfectly round bullet with its base square to its axis. The mold should also be easy to operate, with cavities smooth and free of burrs to allow bullets to drop free when the blocks are opened.

Bullets that are of uniform weight can be obtained through proper casting techniques, use of an alloy that flows well to make full impressions of the mold cavity, frequent fluxing and a correct casting temperature, preferably not over 750°F, which will fill the mold, while minimizing loss of tin and antimony through oxidation. A mold cavity can only hold so much metal, and proper casting by making a large sprue and keeping the sprue liquid as long as possible to minimize shrinkage voids in the casting will result in .30 cal. bullets that sometimes vary only + .2 grain out of the mold.

An article by George L. Jacobsen, former Assistant Superintendent, Frankford Arsenal, (American Rifleman, July, 1958, p. 30), summarized the factors affecting accuracy by saying “bullet quality is, by far, the most important factor.” After shooters get through with all their mumbo-jumbo and the bullet departs the muzzle, out of their control, it is only those projectiles that are nearly perfect that arrive at the target where desired and expected.

As reported by Claude E. Roderick in Precision Shooting, Nov., 1977, cast lead bullets, in proper loads and suitable rifles, will group with the famous bench-rest guns of today. Roderick tells of Mr. James A. “Bud” Welch's shooting 100 vds., 5-shot groups, bench-rest, of .103", .081" and .069" with a .32-40 Darr-barreled Winchester High Wall, single-shot rifle. This indicates that outstanding accuracy is indeed possible with cast lead bullets if we can only find the way.

I find it necessary to carefully inspect every new mold I receive. There are many problems in casting I can avoid if I work the blocks over before heating up the lead pot.

Out-of-round bullets mean poor accuracy, so I wipe the blocks clean of oil and, with magnifiers, check for light coming through between the blocks. If there is a gap, look for tiny burrs along the edge of the blocks that will hold the blocks apart. Carefully stone the burrs away and again check for light. Recently, when examining a new RCBS mold, T found the left side of the slot cut in the sprue plate for the stop pin, cammed the blocks open a hair, and light could be seen. By filing away the metal on the sloping side of the notch, allowing the stop pin to hit in the middle, the gap between the blocks was eliminated.

Holding the blocks with both hands, and the seam towards you, rotate the left block back and forth and at the same time rotate the right block in the opposite direction. If there is movement of the alignment pins in their mating holes, you should be able to feel and see such movement. Look hard at the cavity in the block to see if one side is out of line with the other.

Should there be movement in the blocks, as above, it may be because the rounded ends of the pins are not firmly engaging the holes in the opposite block. Drive the pin(s) further out of the block and again check for movement and alignment. Don't get too tight a fit, as it will be difficult, if not impossible to pivot the blocks apart when casting.

After use or abuse, the holes in the face of the block into which the alignment pigs go will wear or turn up a burr. This burr will hold open the blocks (look for light) and produce an out-of-round bullet. Stone away the burrs with a flat oil stone, then bevel the holes slightly.

So far I have treated only the problem and corrections for molds casting out-of-round bullets. Now I will list other checks to make in the interest of getting better bullets.

1. Be certain vent lines are open into the cavity by tracing them with a sharp, narrow instrument, such as a tiny Swiss knife file. Check both sides of the cavity and both blocks. Generally, two sides of the cavities will be clear and two sides obstructed by metal burrs turned up by the cherry. This will prevent air from escaping, which will produce a bullet with a rounded band. Burrs also tend to make the bullets stick in the cavities. Clean out such vents carefully, and very lightly stone the faces of the blocks afterwards.

2. Using a piece of flat steel or plate glass and 400 grit paper, polish the top of the blocks and the bottom of the sprue (cutoff) plate.

3. Adjust the plate so that it lies firm but flat against the blocks, and so that it turns smoothly without galling. Don't snug the sprue plate pivot down too tight. When casting, let the sprue harden fully so it will cut clean without tearing, or smearing metal across the blocks to force the sprue plate upward, causing fins on subsequent bullet bases.

4. Make certain that handles do not contact blocks except at pins. At times, blocks are held open because they cannot pivot fully on the pins.

5. From time to time as you cast, examine the inside faces of the blocks for flecks of lead that will hold the blocks apart and produce oval bullets.

6. When casting, keep the sprue plate swung open until the blocks are closed. If this is not done, the left block and sprue plate will droop and sometimes strike and raise a burr on the right block, or damage the right bullet cavity.

7. If bullets do not drop free (especially with linotype) look for multiple mold seam marks on bullets from the offending cavity. Lap the cavity to remove burrs in the cavity or vent lines, and the problem should cease.

Near perfect bullets can be made and accuracy thereby improved, but one must be aware of the problems and know the solutions. If you are a seeker of the perfect group, you face many problems in getting a concentric cast bullet with a square base. Some of these problems can be minimized if your bullets are marked to index 12 o'clock as they come from the mold. Mark them on the nose by putting a small prick punch mark on the inside of the cavity, or by filing a tiny notch on the edge of the cavity near the nose. This will leave a small bump which serves as a reference to orient the bullet throughout the sizing, loading and firing process. It is removed easily with the thumbnail before firing and does no harm. Upon inserting the cartridge in the chamber, keep that mark in the same place each time (12 o’clock). If there are errors in your bullet concentricity let them be delivered to the rifling at the same place each time.

Now go shoot that quarter-inch group.—E.L.