Modified RCBS Cadet Mold for true 8mm service

  • Last Post 09 September 2017
corerftech posted this 09 September 2017

I started a project a few years back. Now that I'm moving, sold my company, w/o much purpose, I have immersed myself waiting for my home to sell!


I took some machine classes at local college, got my certificate. Doesn't make me good, just certified to turn a machine on and not lose a finger. For my final exam last class, I decided to build a compex part, a work holding 4 jaw sub-chuck for my old clausing lathe. Got an A plus, then it sat. The chuck ws designed to be precision adjustable for holding mold blocks for cutting and mods. Its been ground to the nth degree, its as square as a device can be and measures well. Its been sitting for several years, I bought a newer lathe and the spindle wasn't adapted to D1-3.


Ignore the rust fingerprints. They are 3 plus years old...... I oiled the thing heavily but nature took its course.

A project over in the single shot world which I will bring this way when further along and more tuned to CBA..... has had me put the device into service. Today I modified an RCBS cadet mold 310-120, for 8mm service with a grease groove. I didn't even mess it up! Got the first cavity correct the first time, get to keep the second cavity as is for a real 310 heeled bullet. Not screwing up for me on the first shot is a welcomed experience! 


I have attached some pics of the thingy--- the mold cut and a sample.

I needed .325+ for a project pea shooter and this was a standing candidate. Its also supposed to serve sized to .323 (which I may open the other cavity to at some point rather than size .004) for a 32-20 cadet which I have opened the neck/throat to 8mm as a quasi-wildcat 8mmx32-20. Actually trying to make the cadet shoot proper with its 32-20 chamber. The bullets fall from the mold, seriously like jump out. Ive never cast with a mold that they fall from like this. And they fall perfect. And they fill out. And they are a perfect form of the cavity (which I molested nicely but still will be amazing when sized.)


Had a good day today, haven't been having many. The moving cross country, sale of my business, purchase of a new home in the east, selling my home, packing, not packing........ days suck and I feel a bit w/o purpose. Stir crazy I guess. This helped me a bit.

Thanks for letting me blow off steam.


The work holder uses precisely ground t-nuts, ground chuck jaws, extremely square. The Jaws simply get finger tight and then you tap with a deal blow to shift the mold as precisely as .0002  (when the jaw tension is right) Im able to dial out all but a could ten thousandths on the existing mold (or at least I was able to today( The RCBS mold was less than concentric and it is now much closer. The falling bullets speaks volumes to the concentricity. Additionally the system allows me to remove the mold block completely, cast with it, take it apart, install in chuck, not lose ANY references of ANY KIND, dead blow a few taps and dial right back in. Ask me how I know.......LOL, did it 3x today. After I figured out the front band was in need of another .002 depth and the driving band was a bit tapered due to my tool flex (will do better next time). I attempted to correct the taper at driving band and added the depth and a bit of width to the front band.Made me happier when all done. It was much fun and I intend to make a habit of screwing up more molds that are already screwed up. And I have more than a few of them that are buggered from Lyman.........


I now have even more respect for Eric at HP Molds as he has this tuning down to a science. He can be my hero.

The two specimens are from the mold (top) and the bore slug that it needs to conform to.

The test chamber #1 cutaway is of a cartridge I'm wildcatting in bottleneck form. The throater/neck was DESIGNED for the 8x32-20 with a thin neck wall and .323/.324 bullet. I adapted the throater to the bottleneck attempt, neck wall is a bit thick but the bullet fits nicely in the throat as cast (will fit better at .325 sizing next week when die arrives)


Test chamber #2 cutaway is a variant with long tapered body. Throat is set for a 190-200 grain .322 bullet. Bad news but the body form is correct for the purpose.


Not to digress off topic, but using several form tools and generic chamber reamers to accomplish the prototype work. At some point the throat/neck will adapt to the final format chosen via custom reamers.

Sharpie marks indicate roughly the end of the neck with relation to the bullet position in throat.


Bottom line (staying on subject) I have two chambers I cut a new mold dimension for with the crap I built in machine school that I figured Id never get around to use and didn't know if my design was valid. It is, its dials in like butter, repeatable, smooth, strong, solid and versatile. 




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Eutectic posted this 09 September 2017

Nice work!

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Ken Campbell Iowa posted this 09 September 2017

great stuff !!  ... i like that tapered base band .... might be just the right thing !! ...  and that 4 jaw looks perfect for smaller work like molds .

what brand and size boring bar ??

when you get out in the humid east you need to really protect against rust .  my favorite  is * fluid film * ... a waxy lanolin ;   from napa .


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corerftech posted this 09 September 2017

The home I bought in Tennessee in the garage area has a workspace isolated, two of them. Th central bac has nearly rusted through the canister, a few other things I noticed are rough too. I'm freaked out by my machines getting killed by rust. My lathe is filthy but rust free. The tool has been three years with a film of oil and the rust is like a patina, no more. I'm moving to a whole new way of rust!


used a 6mm HSS tool  (drill rod looking bar) ground to form. I should have clamped it up shorter, could have tightened up about 1/4 inch more and still had enough length, that may have helped. A better cutter form would have helped too. Luv and learn. . I need to ream a 6 mm ID alum collet, that would have allowed me to extend the tool out further with big support and not crashing the machine.  Don't have a 6mm reamer, bought 6mm HSS on amazon a few years back "cause it was cheap".

Thank you for the protection tip.


edit: figured out what happened to the taper as I re-read ththe above. The tool wore rapidly and broke in. I set DOC based on the initial edge cut (touch off). That's why when I cut the forward band I had to address it 3x. I used same DOC for that section, then had to add .002 on last pass which is the taper value at the base. Hmmmmm.

Ill plan on promoting some extra wear initially. Or maybe the HSS overheated a tad when grinding. Awful small piece to grind. I'll dip more frequently and in shorter intervals. That's what made the taper!!

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Ken Campbell Iowa posted this 09 September 2017

one thought is the hss rod was really green tool steel ... needed hardening after sharpening ...   drill blanks or reamer blanks ( even harder ) come hardened .   just a thought .

yeah, they don't call this the rust belt for nothing .... but you are on the southern edge ... they may not spread salt down there .  ( g ) ...

boring small id is tough because the bar needs lots of undercut to avoid the id of the hole.  that makes the cutting edge thin, which means you have to take off 1 or 2 thou per cut ...which can work harden the steel.... lose-lose .  embarassed



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