My boolits got smaller????

[centershot]

I was checking OD on the batch I cast yesterday and SURPRISE!! They are .002-.003" smaller in OD than any others I have cast with this mold! It is a Lyman 311041 that I've had for years, my alloy is 94-3-3 made up in 100 lb. batches. Same mold, same alloy, what happened? Normally the OD runs .3104", these are as small as .307". Out of 200 or so that I checked only 3 were .310". Any ideas???

[fredj338]

Turn the pot down. Higher casting temp = more shrinkage. Also no mold release, this will often reduce dia as well.

[centershot]

Thanks for your suggestion Fred but, I don't use any mold release and pot temp is PID controlled, steady at 670* F. I'm stumped!

[Geezer in NH]

lead harder than you think????

[reddog81]

Are you sure the PID is working correctly?

How are you measuring the bullets? It's possible your measuring device needs rezeroed.

Assuming the mold, alloy, temp were all the same, the bullets would be the same. Even a different alloy or temp wouldn't cause that much variation in most cases. I'd guess the calipers....

[psweigle]

check your lead alloy hardness.

[runfiverun]

pure lead wouldn't make them .003 smaller.
pure lead doesn't hardly make .003 smaller than lino-type without some other manipulations.

now I have had some molds start to cast smaller over time.
I had a 452664 start getting smaller on me at about the 50-K mark.
I had to re-set the pins re-cut the vent lines and lap the mold.
I don't remember how much smaller it had gotten but it wasn't .003

[pakmc]

I had the same thing happen to me!, I found out that my starnett cal. was off over 50 thousandth of an inch! right in the area that I use(some where between .20 and .458 of an inch) that's when I found a set of gage blocks and sent my starrett off to get overhalled. I can't convence some of my friends that their gages might be out of speck.

[centershot]

I cleaned the jaws on the mike and then zeroed them, just as always. At the time I never thought to check them with a standard but I will do that today. The PID? I'll have to empty it and refill with pure lead to se if it is running true. I've had several thermometers over the years, none of them were accurate enough to trust.

So, now I'm wondering if I had the mold too hot? This mold likes to be run on the cool side, relatively. If I increase alloy temp to 700+ the metal starts flowing into the vent lines. If the PID was accurate at 670*F would it be possible to cast fast enough to increase mold temp to the point that the boolits s were shrinking .002-.003" without showing the "spikes" from flowing into the vents?

[44man]

You can tell if a mold is too hot. The boolit will be smaller 90° to the parting line and larger near the line. Boolits will be more out of round. Your boolits will start to frost.
Let boolits age before measuring too. With antimony and tin, they will expand some. Air cooled takes longer.
I have a Mitutoyo that reads to .0001" and a 61 year old Moderntools caliper made in Japan that I can still read as close as the mic. Can you believe some calipers are made from plastic today?

[243winxb]

check them with a standard, do that today. Hot or cold dont make a .003" difference.

Unless the pot was over 900 degrees. But then you would have frosted bullets.

So, my guess is a measurement problem?

[centershot]

You can tell if a mold is too hot. The boolit will be smaller 90° to the parting line and larger near the line. Boolits will be more out of round. Your boolits will start to frost.

That is it, EXACTLY!!! Thank you 44man!

[44man]

Making my own molds has taught me a lot about expansion. A crazy trip I did not expect. I still have trouble making a cherry the right size and much has been luck.
I have a hard time telling everyone the cavity is not a hole in a block. It is an edge of metal that expands out. I get round boolits by getting the mold hot and putting the cherry in to turn with a wrench to remove more metal. Might temper my cherry too much. It works though.
If your mold is too hot, your boolits are smaller. More in one direction too.
Molds are cut with a coolant and not at casting temps.

[Shiloh]

Already stated, cast as cool as you need to get good fillout. Seems to work for me. There are two molds that i ned to crank up a bit.

Shiloh

[JonB_in_Glencoe]

I have a Lyman 410610 mold that I need to cast at a fast rhythm, so the mold temp it higher than is typical, to achieve a slightly smaller diameter. The difference in size is about .001 from boolits that are cast with the mold at a typical temperature.
The main reason is for getting the GC to fit nicely. Shinely boolits on the left were cast at a typical temperature. The frosted boolits on the right were cast from the mold at a higher temperature.

[TomAM]

The Perfesser posted an excellent study here years ago where he measured the cavities of 375+ degree mold blocks using an inside micrometer. He tested aluminum, brass and iron blocks.

He proved the same results that I found; that all cavities expand when heated. And more importantly, while aluminum and brass cavities remain quite round as they expand, iron expands inconsistently to a larger, but out of round cavity.

There is a popular theory that increasing the temp of your melt eventually produces smaller bullets. Many highly credible casters have observed that result.

But the undeniable fact is that mold cavities expand as the block is heated. The hotter, the larger.

[243winxb]

Thread back from the dead. 02-28-2017, 01:34 PM