Anyone with experience making bullet molds using the lathe and boring bar method?  Could use some advice. Shapes are limited but John-Boy posted some interesting designs.

Trying a .38 caliber bullet with a bore rider design. Pictured are the molds I have tried (mild steel), nose reamer, boring bar, and finished bullet. Have a CAD program, so can predict weights pretty well as discussed here earlier (359 grain predicted, 355 actual).

Problems so far:
Venting groves too deep, 0.003” is too much, getting a flash.

Not getting mold perfectly centered in the lathe. Need to ream pilot hole to indicate center. Drilled hole too rough. Off center and bullets are hard to drop.

Controlling spring-back on the boring bar. Using numbers on cross feed dial, one direction and multiple passes, but can’t seem to get consistent groove diameters. No way to measure until you cast a bullet.  Probably lack of machining skills. Some bore rider groves are too large; have to seat deeper in the case than desired.

Surprisingly, the bullets shoot somewhat better than my factory 335 grain mold. About the 1.5 minute range with black powder. Going to try again to see if I can get it right. Third time is a charm. Any comments would be appreciated.  
Chuck

Chuck,
I modified a Lee aluminum mold from 32-20 to 310 cadet. The aluminum cut cleanly with a tool that looks like the one on the right in your picture. 

I used an indicator to center up the cavity to nary a wiggle. The front band was cleaned up and enlarged a bit, the middle band was enlarged to bore size, and the gas check part was enlarged to 311 to fit the case neck. 

This was my first try & I didn't cut the middle band quite far enought forward to clean up the band completely. The bullet shoots well, however. If I do this again, I'll clean up the bottom of the bullet grooves with a light cut and make the front band a true bore riding diameter.

The pics are of the mold and a couple of bullets from my junk pile, unmodified cavity on left and modified on the right.

Regards, Ron

Very interesting read Merle, I might have to try that.  How do you determine what the bullet diameter needs to be before patching and what to use as a patch paper?

Custom mould makers are great, but for the folks in the cheap seats and for those who just want to experiment or cast a few bullets for something odd, having some LEE moulds hanging around is the way to go. I cut 5/16 slots in the sides to fit small Lyman handles, profile the shape I want on the lathe in a smaller diameter, cut 3/4 of the turned profile away and bore a hole that has been counter drilled to leave a minimum amount in the hole to be bored. Make sure the cutter is relieved and set above center, or it will spring into the work, not away. Measure carefully or design the bullet so that you start cutting from a known dimension and cut as deep as you need to. Since the blocks are aluminum, the cutter can be turned from a good grade of steel bolt for a one-time use - we're not in production here.

I've cut moulds for a Ross (.292"), a Belgian Spencer, a Remington DB derringer, heeled bullets for .32 Longs and Extra Longs, an Evans, and a Sharps & Hankins. 

The cutter will give you a flat area on the nose of the bullet unless you have bored the pointed nose with another cutter and are just relieving the curved surface or the grease grooves. Be sure to relieve the sides of the groove cutters too, or they'll gall. Sharpen the cutter so it scrapes, rather than digs in, as the blocks are soft material. If you get bending, rather than cutting, check the height of the cutter in the bored hole or the areas that need more relief. A mould with an off-center hole can be centered by lining up the two mould parting surfaces on either side of the hole with a sharp center sighting in two positions 90 degrees apart.

I keep an eye out for cheap LEE moulds at gun shows just to keep around for cutting the occasional odd mould. If I screw up and cut one too big, it goes back in the junk box to be cut into something with a larger diameter (but correctly, this time). And if I really screw up, since they're cheap and light, it takes little effort to toss them into the trash.

For a carbide boring bar, you might want to check out this site, (You need to Login or Register to view media files and links), I have purchased from this company and been very happy with the tool I got. You will have to call him to make an order and my guess is that he can grind the tool to your specs as to the angle on the sides and radius on the corners. And his prices are pretty good also.
Sam

I've done some re-cutting of existing moulds, and have found that for limited use, re-ground Allen wrenches are hard to beat for boring bar material.  I hold them in a piece of drilled out round stock with a couple of set screws, and can clamp the round stock in my tool holder.   

David

And the same magazine that back in the nineties told you how to build your own single shot precision benchrest rifle from scratch, you ca nnow get article reprints from midwayusa.

Hello, This is a little different...Back in the early 70's, I needed a heeled .22 bullet for my rimfire-reloads...this could be a story by itself,  Anyway, I was attending a vocational high school & used two aluminum blocks about the same size as a single cavity Lyman, dowelled together for nice slip fit.  A small pilot was drilled on center of parting line (1/2 hole in each block face).  Next I turned up a tool steel "bullet" complete with heeled base a few thou. oversize to allow for shrinkage in casting. After hardening & polishing,   This was placed on pilot hole a little below top surface of block, the other block mated, & whole works placed in a 20 ton Hyd. press & blocks brought together.  I let it "dwell" for awhile under pressure to let metal move & when opened, there was a mirror finished cavity in both blocks.  I milled off top to heel base, made cutter, & was in business.  I got the idea for this from Lee mfg.  They had just come out with their moulds & advertised this "coining" process was how they achieved final size & finish.  I don't know how this would work with larger dia. bullets..probably have to make up larger mould block blanks to allow for distortion, & mill to size after.