Custom Bullet Mold

jbolt

Active User
H-M Supporter Gold Member
Joined
Dec 3, 2013
Messages
1,844
So finally getting to projects that make things other than tools and equipment.

I'm posting this in the projects area since it involves making a custom form tool.

I shoot a sport called Metallic Silhouette which is shot off-hand (standing) with no support, slings or special clothing. Targets are metal silhouettes of chickens, pigs, turkeys and rams set an different distances. There are several disciplines ranging from air rifles with targets out to 60 meters and high power out to 500 meters. One of the disciplines I shoot is lever action pistol cartridge with a .357 lever action rifle. I cast and shoot lead bullets with this rifle. Most commercial molds for the .357 are wad cutters or semi-wad cutters. I have not found a commercial mold with a round nose that can be gas checked. Pistol cartridge silhouette is out to 100 meters and a few of the commercial semi-wad cutter designs do well but I wanted something with a better ballistic coefficient.

There are several companies that will make custom molds from your designs but they can cost $200-$300 per mold. I set about to make my own. Lee Precision offers mold blanks that come with handles so I ordered a pair of those to get started. Lee Precision also has a guide sheet for creating drawings for them to make custom molds for customers. Armed with this info I set about designing a bullet.

This is the final design. These will be powder coated so I chose to use the Lee small lube grooves instead of a large lube groove or no lube groove. The theory is the bullets will be run through a final sizing die and I wanted the body to have a little room to compress without elongating the bullet if it had no grooves while keeping a larger surface area for barrel land engagement. The target weight with range lead & gas check is 155-160 grains.

357158-RNSIL.png

To cut the mold I decided to make a one flute form tool from O-1 drill rod. Several HSS tool bits were needed to cut the various grooves and nose profile.

Tools from left to right are (1) basic turning/facing tool. (2) Nose form tool. This tool has a double radius, .075 at the tip and .312 beyond. I printed the profile at full scale, glued it to the tool bit blank and rough ground by hand on the bench grinder. Finishing was with a diamond bit in a die grinder. (3) Case crimp groove tool at 15 deg with a 90. (4) Lube groove tool, each side is 26 deg. (5) gas check relief tool at 3 deg.

20180728_091537.png

1/2" drill rod turned to .359" ready for the nose form.

20180728_085931.png

Nose profile cut.

20180728_090742.png

Hand sanded w/320 to .358"

20180728_091129.png

Crimp groove cut

20180728_092244.png

Lube grooves cut

20180728_093008.png

Gas check relief cut

20180728_093728.png

Final profile

20180728_094141.png
 
Last edited:
Off to the mill. First order of business is to remove half the diameter. I left .002" for final honing. Note the adjustable parallel under the toll to discourage any deflection.

20180728_102324.png

Next is the side relief cut. I left as much as possible to maximize the strength.

20180728_104820.png20180728_110854.png

Next was to hand grind the rest of the reliefs. Not pretty but it does the job.

20180728_110906.png

At this point I hand honed the flat of the cutting edge on a 400 and 1000 grit water stone to remove any burrs at the cutting edge.

The tool was heat treated and tempered to approx 62C if I did everything correctly. I used the Brownells anti-scale powder for the first time on this part and was pleased with the result. It could be a little better but being the first time use I was not sure on the best procedure for applying the powder. The steel needs to be heated to 500 deg and then coated. I ended up with a few spots where it was too thick which cracked and spalled off during heat treating.

20180729_135751.png

The tool is now hard. The edge held through the heat treating so no need for further honing.
 
To cut the mold I made a tool holder from a 1" square aluminum bar held in a tool post holder. The aluminum wad drilled and reamed in the tool holder using the lathe chuck for drilling and reaming. This ensured the form tool would be on center and established the zero or final cut dimension. A couple of 10-32 screws in the side of the aluminum lock the form tool in place. I also turned a centering tool out of the same drill rod to use in the tool holder to assist is aligning the mold to the cutter.

Reaming the tool holder.

20180729_142233.png

To hold the mold halves I modified some soft jaws for my 3-jaw chuck to replace two of the jaws on my 4-jaw chuck. This is exactly why I purchased a 4-jaw chuck with two-piece jaws.

Here is the mold aligned and pre-drilled ready for cutting the profile with the form tool.

20180730_203829.png

The form tool was set to plunge cut the minimum bore diameter of the largest bullet groove and then advanced .03" at a time then cleared of chips until I got to the end of the pre-drilled portion. I then advanced in .01" increments with the final depth in a couple of .005" increments. Once the depth was cut the form tool was advanced into the side of the bore to create the grooves. Total side depth is .016" which was cut in three steps.

I only cut one cavity for now. I will now cast some bullets to verify they cast at the correct diameter and will accept gas checks.

20180730_204532.png

Ready to cast some bullets.

20180730_205657.png
 
Nice pictures and pointers.
The adjustable parallel under the reamer during cutting really caught my attention.
Thanks
 
The first run was not successful. The bullet is .013" under size and the groves are not well defined. I'm going to attempt to re-cut the same cavity.

I just don't have a good way of measuring the cavity with the grooves. My smallest bore gauge only goes down to .350' and the minimum ID for the crimp groove is .326". I may have to get a set of pin gauges.

20180731_140525.png
 
Maybe just take a piece of aluminum and turn it to lube groove diameter for use as a gauge.
Or .001 under.
I would be pretty hesitant to stick a steel pin gauge in an aluminum mold.
 
Could it be your cavity cutter? I think if you cut the tool like a single-flute reamer you may be able to keep the groove definition. I didn't realize the first read through that you removed a lot of material from the back side of the cutter for clearance. How is the roundness? Looks like you did a good job with the mold blocks, I imagine they're going to come out nice and round.
 
for holes under 0.5", use a small hole gauge. similar idea to bore gauges, but consist of 2 rounded fingers that are forced apart by a cone. They come in sets of 4 from 0.125 to 0.5". Super handy for small holes :)
 
Maybe just take a piece of aluminum and turn it to lube groove diameter for use as a gauge.
Or .001 under.
I would be pretty hesitant to stick a steel pin gauge in an aluminum mold.

A steel pin is not a problem as long as you are not forcing it. Aluminum is sticky so aluminum on aluminum is probably not the best way to go. If one was concerned about marring, a brass or bronze pin would be better.

The more I thought about it a pin gauge will only tell me what the minimum bore diameter is. I would be assuming the groove diameter is correct without ever having measured it since I have no way to do that with the basic measuring tools I have. The neutral rake form cutters used to make the grooves may not be cutting to the actual depth shown on the digital readout.
 
Back
Top