A question od DIY mold fabrication - no meplat + lube grooves.

[flynth]

I'm making a mold I mentioned in another thread on this forum (made of 7xxx aluminium, sprue plate borrowed from a Lyman mold).

Prior to making the blocks and the cutter I read lots of threads and I watched lots of videos of people making custom bullet molds.

However, I never saw a solution shown to the "meplat issue". Many bullet designs are fine with having a meplat (flat front), but I'm trying to replicate a historic design so I would like to not have it.

Unfortunately the problem is when you typically make a lathe bored mold with a form cutter that it is necessary to feed the cutter in, then move it sideways at least for the depth of lube grooves (for the lube grooves to be formed).

This results in some portion of a round nose profile cutter to end up right of center. Relieving that portion of the cutter results in a meplat.

The only solution I can think of is to use two cutters. One you only feed forward for the tip, and the other for the rest. The problem with this approach is aligning both cuts without seeing them (in a cavity).

Did anyone manually cut a mold for a bullet with no meplat, greese grooves and nose diameter starting same as grease groove outside? If yes, please describe how?

I'll be attempting the two cutter method.

[garandsrus]

The older method of cutting mold was with a Cherry and a vice that closed both mold halves at the same time over the cutter so the cut was always full length and wasn’t bored.

[17nut]

All NOE moulds are cherry cut on a mill one half cavity at a time, thus no meplat.

[flynth]

All NOE moulds are cherry cut on a mill one half cavity at a time, thus no meplat.

Wow, one half at a time? There must be some serious precision involved. What is the target precision in the depth of cut direction?

I decided to use one cutter after all. When I did a test cut in a piece of aluminium stock I saw the resulting meplat was pretty small and I could live with it for this attempt.

Perhaps next time I'll try mill cutting one half at a time.

I cut my mold in the 4 jaw on a lathe. I aligned the halfs to better than 2 tenths(halves were surface ground to same height). I don't think I can achieve that on a mill. However, maybe one doesn't need the cavity centered that well.

Here is my finished mold and a good example bullet it cast.
https://i.ibb.co/NtDtNjc/20210812-011331.jpg