Bullets diameter increasing after they are cast?

[HP9MM]

On 11/6/16 I cast 125 bullets with my Lyman .429421 mould and dropped them in ice water. Initial BHN was 10 and increased to 15 now. Today I sized & lubed them in RCBS S&L using the .429 sizing die. Seemed that more metal was being moved so I miked the unsized bullets. They were running about .435 to 8 in diameter. This is new to me. Anyone else had this experienced? Did I do something to cause this?

Merry Christmas!

[BK7saum]

What diameter do they measure as cast from the mold? If you mean 0.438", then I think the mold isn't closed all the way. Are they wider perpendicular to the parting line than with the parting line?

[17nut]

How did they mic as cast?

Why ice water?

Have you looked at your mold halves with a magnifying glass?
Maybe a splatter of lead is stuck there and making the bullets large and oblong.

It is very rare for Lyman moulds to cast oversize and once in a full moon for ones that casts that large.

[HP9MM]

Good advice.

[swheeler]

An alloy containing antimony will grow as aging up, adding copper to it seems to increase growth. After a month passed they probably stopped growing in diameter, though .435" seems pretty large? without knowing as cast diameter we are guessing but .001-.0015 is pretty common in COWW alloy. Caliper measurement?;)

[Phlier]

Here's a great thread on how different alloys will effect casting size... Think it also talks about certain alloys increasing in size with age, too. Some alloys will also get harder with age as well: http://castboolits.gunloads.com/showthread.php?192192-How-does-alloy-mix-affect-casting-size

[DougGuy]

Age hardening produces growth in diameter with alloys containing antimony. The growth in 44 and 45 caliber boolits is normally in the .0003" to .0006" range, the longer and heavier the boolit, the more the growth. Do they shorten in length while growing in diameter? I don't know. It is very common to see growth in excess of .0015" in 500 S&W heavyweights as well so the growth seems to increase exponentially with caliber and length of the boolit.

I do a lot of cylinder throat work and consequently get a lot of dummies sent in by customers so I have a very wide sampling of cast boolits and I have paid attention to their diameters when I get them and it has helped me to adjust finished cylinder throat diameters per caliber according to what the majority of folks here size to. I have learned that sizing the throat too close to boolit diameter will produce a situation where dummies chamber when sent in to me, but in 6 months, those same dummies meet resistance going into the cylinder throats. For this reason I like to have .0005" to .001" over boolit diameter for "wiggle room" so that the customer doesn't have issues with fitment some months down the road.

Along those same lines, let me mention that in the 480 and 500 calibers, it may be necessary to adjust one's loading cycles to take into account this growth and size the boolits within a time frame prior to shooting and not allow them to sit on a shelf long enough so that the growth doesn't allow them to chamber. Reaming 500 S&W cylinder throats to .5025" ~ .5028" to accomodate cast boolits sized to .500" initially is about the only way to sure fire take care of the situation, but one must also remember that with an increase in resistance, comes an increase in pressure. I would rather see throats sized closer to groove diameter, .5015" for example, and the shooter size to .501" before loading and then use this ammo before it grows beyond throat diameter, for those loads that are approaching max pressures.