machining moulds

[indydave]

mould machining dimensions :roll: ok what are final OD's for for a .452 .503 moulds i have old blocks, a machinist buddy, and ideas :coffee: just no idea for the cold OD so its right when casting. i want to make a mould similar to a 460-495 grain no excuses bullet with an extra lube groove
thanks
indydave

[dubber123]

Well, we'll see what you get for answers. I'm having one cut right now, looking for a .452" to .453" boolit, so I specified a .454" cavity, figuring .001" to .002" shrinkage. We'll see if I guessed right. Welcome to the forum.

[BABore]

It all depends on;

- Mold material
- Venting method
- Bullet diameter
- Bullet length
- Bullet design (SWC vs ogival nose)
- Lube groove confiuration
- Alloy and pouring temperature
- Pouring method
- Moon phase and tidal conditions [smilie=1:

I've had to cut some cavities right on size, to 0.003 over. You will sometimes get a tapered condition where the base will come out smaller than the front band. Generally, if you cut the cavity to;

0.0005" over for 30 cal.
0.0005 to 0.0010 for 35 cal
0.0010 to 0.0015 for 37 thru 44 cal
0.0015 to 0.0020 for above

it will give you a decent starting point. GC shanks can be a little quirky. I use the Gator max shank diameter and generally add 0.002" to get them to come out right. You will need to consider how you size things based on your cutting method. You can undersize a cavity with lathe boring and recut it if necessary. Only time is wasted here. If cherry cutting you are better off oversizing the cherry. You may waste a block set, but you can't make a cherry grow. The cherry is the expensive part here. You can regrind it if you find yourself being way too big.

You will find that just when you think you have things figured out and mastered, you'll get thrown a curve ball.

[leftiye]

I'm putting an extra front driving band on a Lyman 225238 mold right now. I measured the mold to see how big the mold was as contrasted to what size the boolit comes out. To get a .226" casting, it looks like you need about a .228 mold size. Bigger boolits should shrink more.

Maybe measure some of your other blocks made of the same material you want to use to make this new mold, and then cast some boolits in those blocks (that you have) of the alloy you plan to use in the new mold and see how much they shrink?

[JIMinPHX]

If cherry cutting you are better off oversizing the cherry.

The exception to that would be if you run the cherry in a CNC mill. Then an undersized cherry is the way to go. You can always open up your diameter by interpolating a small circle with the cherry in the blocks. This will also be likely to give you a better surface finish than a single crush cut with the cherry because of the reduced chip load.