Custom Bullet Mold

[jbolt]

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.

I tried re-cutting the cavity and discovered some errors on my part. First, when I did the initial plunge cut I failed to account for the DRO being set for diameter and did not account for that so the minimum bore was cut over size from the get go. This explained for the loss in definition of the grooves but did not account for the cavity being under size. When re-cutting I also found the relief grind toward the base of the bullet was not deep enough and interfering not allowing the cutter to engage further. It also flared the base of the mold.

At that point I took a good look at the cutting tool and re-honed the edge, improved the relief and did some fine detailing with a rotary tool to improve the cutting edge. After that I cut another cavity. This time I paid better attention to how the cutter was performing and found that with the large neutral rake cutting edge the cutter has about .002 of spring. This time I ran the final cut several times allowing for the spring of the tool until no additional material was removed and I could feel the cutter just starting to make contact at the final dimension. During the final dimension cuts I would let the cutter dwell on the part for 2-3 minutes at a time before clearing, cleaning, lubing and repeating. I did that about eight times I think before I felt it was fully cut. I didn't have time to cast any last night so I will try today and if it is still under size I now have a better feel on how much more I would need to cut.

Here is the second cavity. You can see the groove definition is much better.

 

[jbolt]

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

That is an interesting idea. It would be difficult to try and measure the peak of a tapered cut but I suppose you could preset the hole gauge to a dimension and use it as a feeler gauge.

 

[mattthemuppet2]

yes, they have the same disadvantages as bore gauges, but they are smaller at least! For gauging the bottoms of the valleys I think your only option is to make a form gauge (like a thread gauge) and use that.

 

[jbolt]

First casting came out .004" under size so I put it back in the lathe and recut it to the correct size. These came out as I was expecting.

Sent from my SM-G955U using Tapatalk

 

[mattthemuppet2]

nice! How do you QC them, short of firing them out of a gun? I assume that any small variations in the casting process (fill, voids, I dunno) will have a large effect on the ballistics?

 

[jbolt]

For competition use bullets are sorted by weight. Being made from scrap lead pulled off the berm at the range the alloy composition can vary which affects mold fill out, weight and hardness. Voids are uncommon but can happen.

Ballistics is a little more complicated but in general terms is a function of bullet weight, length, shape, velocity, spin and barrel length. At distance some other factors are altitude density and angle. Being a pistol cartridge bullet the effective range out of a riffle is around 200 yards. A flat faced wad cutter type bullet will obviously be much less due to the high drag but these are intended for short distance use.

 

[mattthemuppet2]

cool, thanks for the info. I'm guessing "grains" is the unit of weight used?

 

[shooter123456]

cool, thanks for the info. I'm guessing "grains" is the unit of weight used?

Yes, it is common for measuring powder and bullets. 1 grain is 1/7000 of a lb.

 

[MarkDavis]

Matt,
A bullet mold will usually get better with use, it takes a few heat/cool cycles to cook all the cutting coolant out of the blocks, and sometimes little quirks with temperature of the melt, and time timing of casting, help make pretty uniform bullets.
That second bullet looks pretty good coming from a fresh cut cavity.

If you really want to fall in bullet casting hole, check out castboolits@gunloads.com

 

[jbolt]

That second bullet looks pretty good coming from a fresh cut cavity.

The last photo with the two bullets, the top bullet is from the first cavity which was over bored, the bottom bullet is from the second cavity which was done correctly. It was a side by side comparison I failed to describe.

I scrubbed the mold in hot water and dish soap after machining and then soot the mold cavity with a wood match. It takes about 10-20 castings to get the mold temp right before dropping good bullets.