Lyman sizing die sizing too small?

I have the Lyman lubrisizer with heater and have made about 1200 9mm 120gr truncated cone projectiles. They have all already been loaded and shoot great all sized with a .356 sizing die but with some leading I got to looking for the problem and I have found that my sizing die is actually sizing them to .3555 I did pull a bullet to be sure it's not be sized by the case and went ahead and measured a fresh sized one to get that measurement. I just want to know if this is standard? If I buy a Lyman .357 die will they come out .3565?

Not complaining as they do all shoot great and accurate and the leading isn't bad to me I'm just curious about the sizing dies. I do get that technically if we're rounding then they are .356 Has anyone else noticed this?

Have you measured with more than one micrometer? I have Lyman H&I dies in .356, .357 and .358 and they are spot on as I measure. It's been a very long time since the .356 or .357 were used. I load for 6 different 9MM's and size to .358 for all.

Better still is to use your Michrometers as comparators in conjuction with a set of pin gages. Measure .356 pin then bullet. Otherwise it a simple matter to polish out .0005-.001 from the die.

How do you polish out some and keep it round?
i just ordered a .357 die but I'll double check the sizing with another micrometer.

It is common to have off the shelf bullet sizing dies not be spot on the marked dimension. We you discovered what we all have realized in due time. I once bought three .313 Lyman dies trying to find one that sized bullets .313. I finally had to have Buckshot make me one and it was spot on.

I bought my first Lyman .452 dies back about 1962. I sized many thousands of bullets with the die, until one day I measured the bullets. That Lyman die was giving me .453 bullets. I never knew it and as happy as a clam at high time.

The salient fact is that if it is working for you keep at it.

How to hone a size die
by Buckshot
Oft times we find ourselves needing a bit more girth in a bullet to please a particular firearm. And, as
sometimes happens the size we need isn't available or we don't want to pay for the custom manufacture of
one. You can do this yourself and accomplish very accurate results for just a few cents worth of materials
(not counting the size die) and a bit of time.
What you will need:
1) A size die that is as close as possible to what you want
2) A length of steel rod that is close to 3/4 of the diameter of the existing die, and long enough to
protrude at least 2" beyond both ends of the die.
3) Wet or dry emery paper of 320, 400, and 600 grit. If you do need to remove more than a couple of
thousandths you should also include 220 grit. Actually the 400 will finish the inside well enough, but
hitting it with a bit of 600 sure slicks it up.
4) Oil. Most any oil will do.
What you do:
The paper should be cut long enough to extend out either end of the die, almost as long as the steel rod.
Wrap your starting coursest grit paper around the steel rod a couple times and apply some oil to the paper.
Insert the covered rod through the size die. With just your thumb and a couple fingers on each end of the
rod, roll it up and down your thigh (while sitting) applying only mild pressure. The reason for using a rod
as large as possible, is to keep from tapering the inside of the die, by having a slender rod bend under
pressure.
This will get your pants leg fairly well oiled up, so use old pants. Or you can staple a bit of cloth to a
length of wood. Most any surface that the die can turn on is fine. I use a piece of mud flap screwed to a bit
of 2x4, and clamp it in the vise, and it's a good working height.
Roll the steel rod occasionally as only a small portion of the paper is in contact with the interior of the
die. You should also swap the die end for end every now and then to make sure the metal removal is as
even as possible. Remember the throat of the die is tapered to admit the bullet and we're only wanting to
open up the actual sizing portion of the die.
When you check your work you don't need to put the die back in the press. Just drill a hole in a board
bigger than the bullet and place the die over it. Place a bullet in the die and tap it through. Remember to
leave a bit of metal to remove for your polishing down to final size with the finer grit paper. The first
time I did this I just took it down to where I wanted it without thinking of the finish. It works, but you do
need a bit more effort to get the bullet in and out, and it just isn't the right way to do it!
Your existing plunger will still be fine in the honed out size die, unless you opened it up several
thousandths. Even then it may still work fine, but you'll need to pay more attention to the lube consistancy
and the amount of pressure you exert on the lube reservoir.

Quote:

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Originally Posted by Chris_h

How do you polish out some and keep it round?

...SNIP

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I have some steel rod scraps, that are about .200" dia.
I cut a 1.5" slot in the end of a rod that's about 8" long

I cut a strip of wet/dry sandpaper (220 grit) and wrap it around the rod, the strip needs to be the correct length, so when wrapped, it fits very snug in the die. I add some oil, I spin it with a battery drill. I generally go through 3 or 4 pieces of sandpaper. You need to clean up the die and test it periodically, to see the progression, When I get to were I need to be, I use a worn piece of sand paper with flitz to polish.

Thanks for this! I'll use this in the future. I hadn't even thought to search to see if it was possible to open them up a bit.

A I got my new Lyman sizing die .357 and I sized a couple and all my bullets seem to measure at .355 or .36 still. I must have bad calipers or am doing something wrong

Update on this^^^^
I used my other micrometer and got the right readings. My old die was a touch small and my new die is a touch big.
So I'm good thanks all