Heat expansion in a iron mold

[greenjoytj]

I have read that heat expands a mold lengthwise, so bullets that drop from it measure wider diameter along the part line than a 90* perpendicular to the part line.

I have a Lyman 452664 four cavity mold.
Bullets dropping from this mold when sized in my Redding Lubri-sizer .452” die get too much lead swagged up the ogive at the part line.
This prevents the cartridge rim from seating onto the cylinder preventing rotation.

I cast these bullets last summer an just now statted to load and shoot them, there by discovering this problem.

All cartridges were plunk tested in a gauge but not in the actual cylinder they would be fired in.

I’m I casting too hot?
Making the mold grow longer creating bullets with more out of round distortion.

Maybe multiple cavity mould are a bust and I should have gotten a double cavity.

I could try just filling cavity 1 & 4, to try to reduce the mold expansion and out of round state of the dropped bullets.

Alloy used is Rotometals 20:1
Furnace is a RCBS ProMelt-2 PID controlled.

[M-Tecs]

I have read that heat expands a mold lengthwise, so bullets that drop from it measure wider diameter along the part line than a 90* perpendicular to the part line.

Not true. Thermal expansion is in all directions. If you have out of round bullets it's not from thermal expansion.

It sounds more like your mold is not closing fully.

Whatever the problem is is not from being a 4 cavity.

What size are they dropping from the mold?

[greenjoytj]

Randomly selected 4 bullets cast last summer in my Lyman 452664 four cavity mold.
This mold casts 250 gr RNFP bevel base single lube groove bullets.
I believe Lyman designs mold to drop at 250 gr nominal using Lyman #2 alloy.
I use Roto Metals 20:1 alloy so my casting were dropping heavier 253 gr + or - 2 gr.
The lightest and heaviest were culled and remelted.

I don’t know which cavity the 4 selected bullets dropped from, I do know it wasn’t C1 as that cavity dropped low weight under diameter bullets that only sized along the part line the sizing die wouldn’t touch the bullet perpendicular to the part line. I quit using C1 and cast with C2,C3&C4.

#1 is .4563”. Parallel along the mold part line and .4535” perpendicular to the part line.

#2 is .4541” Parallel along the mold part line and .4539” perpendicular to the part line.

#3 is .4537”” Parallel along the mold part line and .4539” perpendicular to the part line.

#4 is .4558” Parallel along the mold part line and .4513” perpendicular to the part line.

The mold haves always closed tight. Had they been open slightly a bigger part line would have occurred along with bullets measuring wider across the part line and much heavier.

[M-Tecs]

If that is a new mold and it was mine it would be going back to Lyman. Cavity # 4 is .0045" out of round.

[Conditor22]

Not to slam Lyman but I have gotten and fixed (made useable) several of their 4 cavity molds that were messed up and were given of sold cheap.

SEND IT BACK!!!

It depends on who you talk to as to your results with Lyman

Good luck