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From Ingot to Target: A Cast Bullet Guide for Handgunners©
How to make a HP mould
Some hollow-point (HP) moulds can be pretty hard to find, other worthy designs may have never been offered commercially. The ability to convert a regular bullet mould to drop a HP version of that bullet offers the caster ready access to hard-to-find HP designs, or allows the caster to experiment with novel HP designs that may have never previously seen the light of day.
When you get right down to it, there isn’t really a whole lot involved in converting a regular bullet mould to cast HP bullets: drill a hole for the HP pin, make a HP pin and install some means of holding the pin in place while you pour the bullet metal. The kicker is, that hole has to be exactly centered on the bullet’s axis. OK, so you just chuck your mould up in a 4-jaw chuck, dial indicate off of the cavity to get things centered and then center-bore with a bit of the desired size, right? Maybe, maybe not… virtually nothing about a typical mass produced bullet mould will be square with anything else, much less have any trueness in its relationship with the cavity (it might be close, but it’s doubtful that it will be truly square). Yes, it’s easy to center the mouth of the cavity using a 4-jaw chuck, but since the faces of the mould blocks aren’t parallel or square with the cavity’s axis, the posture of the blocks in the chuck results in the cavity’s axis not being parallel to the lathe’s axis, so the hole might start in the right location, but it wanders farther and farther off axis the deeper you drill (unless you invest significant time and effort into shimming the blocks and dial indicating off of several portions of the cavity).
So, how do we drill a simple hole that is indeed concentric with the bullet so we’ll make a stable bullet that flies true? Easy, we ignore all external surfaces and index off of the cavity itself. This requires that we turn a dummy bullet that snugly fits the mould cavity in question, and use this to guide our work. This can be done 2 different ways: we can make a center-bored pilot that we use to guide our drill bit, or we can use a mandrel to turn the mould on the lathe and center-bore the mould blocks from the tailstock. Examples of each are discussed below.
First, buy the parent mould for whatever bullet design you want a HP for. Single cavity moulds are ideally suited to this conversion and are usually pretty cheap and widely available since most bullet casters want to make lots of bullets in a hurry and sell off their single-cavities to buy gang moulds. The external condition of the mould doesn’t matter, just make sure that the cavity is crisp and sharp. I have always wanted HP moulds for the Lyman 410459 for the .41 Magnum and the Lyman 452460 for the .45 ACP. Both parent SWC’s have proven themselves to be exceptionally accurate, and I was hoping to combine that heritage with an expanding HP for hunting small and medium game (coyote, antelope, etc.). I looked for both of these moulds in HP form for years, and wasn't able to find either one (although I did find a 410459 HP about a year after I made this one). Therefore, I was forced to convert SWC moulds to HP form to scratch this particular itch.
The conversion of the 410459 started off with a piece of ½” drill rod (W-1) and a #27 (.144”) drill bit. The drill rod was chucked up in a 3-jaw chuck and center-bored to a depth of about 1”. This piece was then turned to about .416”, or slightly greater than
final finished diameter (.410-.412” depending on the mould). Next, the features of the bullet’s profile were turned (crimp groove, lube groove, ogive, etc.). The important parts of this step are fitting the bearing surfaces of the driving bands and the meplat of the bullet to the cavity, matching the exact ogive isn’t as critical. Fitting, de-burring and polishing were continued until a snug fit of the pilot inside the cavity was achieved. At this point, the pilot was cut from the drill-rod with a parting tool, and flame hardened with a propane torch (heated to a bright red and water quenched). The pilot was then placed in the mould cavity, the mould clamped in a vice, the pilot hole filled with cutting oil and the hole drilled through the bottom of the mould blocks using the same #27 bit with a hand-held electric drill.
The HP pin was turned from ¼” mild steel roundstock to .142”, so that it would extend to the top of the first driving band when in place. The exposed portion of the pin was tapered slightly (5 degree taper), the tip rounded, and the whole unit polished. The knob was cut from a piece of oak scrap using a 1 1/4” hole saw, and the profile cleaned up on the lathe. The bottom of the mould blocks were drilled and tapped for 6-32 x 3/8” pan-head screw to serve as a keeper. A groove was turned in the pin to hold the retaining clip such that it was a snug fit just inside of the retaining screw when the pin was in place. The knob was installed and oiled with teak oil, completing the HP spud.
Bullets cast from the new HP mould weighed 207 grains when cast with WW alloy sweetened with 2% tin. The bullets dropped very easily from the mould and were visually beautiful, with perfectly centered cavities (better than several of my factory HP moulds in fact). These bullets shot reasonably well, but not to the level of accuracy that I had hoped for. A micrometer revealed the reason why -- the bullets were undersized and nowhere near round, with diameters varying from .408” to .412”. The mould cavity was lapped to
a more uniform and better fitting .411-.412” with 120, 280 and 400 grit silicon carbide. Bullets cast from the larger, rounder cavity shot much better. Opening morning on the Snake River had a mulie doe wander within 50 yards of my position hidden in a basalt outcrop. I launched the 410459 HP using 21.0 grains of W296 over a CCI 350 primer (1320 fps from a 6 ½” S&W 657 Classic Hunter). Her lunge told me
she was heart-shot, and then she circled tightly to her left to come back around to her original position and collapsed. The 410459 HP entered the middle of her left shoulder, just behind the leg, and ranged forward and down, exiting low on the forward edge of the right shoulder. Expansion was positive, with the forward third of both lungs shredded and the heart center-punched. In short, the bullet performed exactly has hoped, expanding smoothly and punching all the way through.
After I completed the mould described above, I proudly described the process and results to my good friend (and pistolsmith extraordinaire) Dave Ewer. He looked at me with that comical expression he gets (all too frequently) when I do something in a more convoluted or round-about way than was needed. When he finished chortling at all the extra work of parting, hardening, hand-drilling, etc., he congratulated me on my success and suggested a
simpler and more straightforward method, and one that allows even more precise alignment of the hole with the bullet‘s axis. Hence was born Method B, to be forever more known in my shop as “Dave’s Method for a Hole in the Head” (the “hole in the head” in this name refers to the hollow-point cavity, or at least that's what he told me...).
Method B (demonstrated on a single cavity 452460)
In this case, work started with a ½” piece of aluminum round stock, which was turned to match the profile of the 452460 mould (similar to that described above, except no center bore, oh and by the way, turning aluminum goes MUCH faster than drill rod). Once the fitting was completed, the mould blocks were clamped firmly in place on the
mandrel with an automotive hose clamp. A “dog” was made out of scrap aluminum flat-stock and clamped onto the mandrel’s shaft to anchor the sprue plate stop pin and
prevent the mould from slipping on the mandrel (this could also be done with a hose clamp). A 5/32” end-mill (.156”) was used to make a plunge cut from the tailstock to start the HP pin channel (a drill bit can wander when starting a hole, so the end mill chosen for the initial cut to insure that the hole was maintained on center). After the initial hole was made, it was reamed to the desired final diameter using a #18 bit (.169”). The pin was turned from ¼” mild steel round stock to a diameter of .167”, set to penetrate to the middle of the top grease groove. The tip was given a 5 degree taper, rounded off, and polished. The bottom face of the mould was drilled and tapped for the retaining screw and the keeper clip and knob were fabricated as described above.
Bullets cast from this mould weighed 186 grains using WW alloy, sweetened with 2% tin. Bullets dropped easily from the mould and cavities were well-centered. Initial .45 ACP test loads were assembled using 5.0 grains of Bullseye and CCI 300 primers. From a full-size (un-tuned) Kimber 1911, these bullets produced a 10-shot group at 50 feet that could have been completely covered by a silver dollar. Yes, this is an accurate bullet.
From a full-sized Colt Government Model 1911, these bullets deliver 1121 fps when loaded on top of 7.5 grains of Unique. Impromptu expansion testing on 2 liter plastic bottles filled with water
revealed that these HP’s indeed expand readily. More formal testing with ballistic gelatin confirmed this. The first shot fired into a 16” block of ballistic gelatin expanded fully and stopped less than an inch from the end of the block. Based on the “wound channel” left behind, the second shot also expanded, but it exited the block and impacted the backstop, 100 yards downrange. The final 3 shots all expanded nicely and stopped after penetrating 12-14” into the gelatin. The four recovered bullets weighed 186, 183, 171 and 150 grains. In short, expansion is positive, weight retention is good and the design flat works.
Advantages/disadvantages of each method: Method B is faster if the gunsmith is only converting a single mould, and arguably results in a more precisely centered HP pin as the cavity itself is turning on the lathe‘s axis. If multiple moulds are going to be converted, it would be advantageous to turn the
mandrel out of steel for greater durability. Method A takes a little longer, but if the gunsmith is going to convert more than one mould of a given design, once the pilot is made, then subsequent jobs are very quick and easy, requiring only a vice and an electric hand-drill (no lathe work), and can be handed off to an assistant to perform. If this conversion is being contemplated on a fixed handle mould, or on one (or more) cavities of a gang mould, then Method A would avoid having to swing the mould in a highly eccentric fashion.
Method B also allows the channel to be cut over a much wider range of dimensions. The advantage of a wider channel (and pin) is that a wide variety of cavity diameters, profiles, etc. can be made to fit a single set of mould blocks, allowing the caster to experiment widely with a minimum of investment. The thicker pin also has a larger thermal mass and won’t cool down as quickly (conversely, it will take longer to heat up). The traditional pin design (.150-.170"), while simpler to make and fit, can also be varied as to cavity depth and taper, but is more limited in terms of cavity diameter. With proven HP designs (e.g. the Keith and Thompson HP’s) this is of little consequence however.
For those that don’t have access to a lathe, HP mould conversions can be performed by: Hollow Point Bullet Mold Service: (http://www.hollowpointmold.com, email@example.com , (541) 738-2479 ). Erik has converted a number of moulds to HP configuration for me and I have been very pleased with the quality of his work in every case. What’s more, Erik offers a variety of different conversions, including multiple cavity HP conversions (Cramer-style and inset-bar style), that allow the caster to make a bunch of HP bullets very quickly.
He did a 4-cavity 429421 HP conversion for me and I can routinely cast 10 HPs a minute with this amazing mould. The 2-cavity Cramer-style HP moulds that he’s done for me can produce 5-6 HPs a minute with no problem.
Cast HP bullets provide the handgunner with excellent expansion properties for hunting medium and small game. Some HP mould designs can be found on the used mould market, some are difficult or impossible to find (or very expensive), others only exist in someone's imagination. Conversion of a standard mould to drop HP bullets allows the caster to have access to these designs. A small investment (of either time or money) can provide a lifetime supply of high performance hunting bullets.
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