Sizing Die question for the Wise Ones

[Mark Conry]

I have just started casting boolits for 40-65.
I am using a Lyman 410663 mould which produces boolits which average .410" in diameter. This is exactly what I want for my rifle.
When the boolit is lubed through a Lyman .410 sizing die, the boolit comes out of the sizer at .408".
I miced the inside of the sizing die at .407".
Why would a .410 sizing die produce a .408 boolit?
Is this "normal" behavior for sizing dies?

[MT Chambers]

While I'm not considered one of the "wise ones", I have bought quite a few sizers that were off like yours, you can open it up a bit and there's lots of info here on how to do this, or keep it and order another. There will come a time when you'll want to try a .408" bullet. I've never found a Star die that was off either from Magna or Lathesmith.

[Bent Ramrod]

It certainly is not as advertised, nor is it the ideal situation, but wrong hole sizes are not exactly uncommon. Most dies will be within a thousandth of the number stamped on the top, but there will be the ones that are a couple or even three thousandths out. If it is new, you should be able to send it back to Lyman for a replacement. If old, a dowel with 320 grit sandpaper should open it up a couple thousandths.

I would suggest that if you do send it back, you might ask for credit against a die of 0.411" diameter. Or if it is old, have Buckshot or somebody bore it out to this diameter. I use oversize dies with my black powder caliber boolits, essentially shooting them as cast. The lubrisizer acts only as a lubricator and the die only holds the boolit as the lube grooves are filled.

[pworley1]

Have you slugged your bore to see what you need? If so, get Buckshot or one of the other machinists on this site to make you one the correct size for your bore. As has already been suggested, keep the one you have. Sooner or later you will need the 408.

[Yodogsandman]

Which alloy are you using? How long after casting the boolit did you size it?

[462]

You said that you "miced" the boolit and the inside of the die.
Did you use a caliper accurate to +/- .001", or a micrometer accurate to +/- .0001", to measure the boolit?
Did you use an inside micrometer to measure the inside of the die? You can't accurately measure a round hole using a caliper with straight edges.
If you are not using the correct measuring tools, you will get incorrect measurements.