Bullets that Gain Diameter

[Taterhead]

I'm looking for some insight about why bullets grow in diameter over time. I've observed that when bullets come out of the sizer, they measure the diameter indicated on the NOE bushing, on the nose.

If measured several weeks later, they almost universally gain diameter.

They range from a hair under a thou to 2.5 thou.

What I can't pinpoint are the conditions that contribute to more or less growth.

Things in common:

Alloy 3% Sb and 1% Sn
Powder coating

Differences, amount reduced through the sizer. Some are heat treated, others are not. And of course the nominal diamter.

Are there rules of thumb that will indicate a propensity to grow vs not?

[DougGuy]

Boolits with higher antimony content seem to grow more as they age harden, I have also noticed particular growth in boolits that are long for their caliber, like heavy boolits for 480 Ruger and 500 S&W, these because they are quite long for their diameter, grow rather quickly and grow a lot compared to shorter boolits of the same diameter.

A note on cylinder throat diameters should be in order here, as they figure into the equation as well. I size throats .0005" to .001" greater than boolit diameter to allow some growth and still be able to chamber the assembled rounds, and also some boolits aren't necessarily perfectly round so a little wiggle room in the throats is a good thing.

However I do not like to size 480 and 500 throats to accommodate growth from age hardening, and I usually recommend sizing throats only .001" to .0015" over groove diameter, and shooting sized boolits before they grow too large to chamber. Boolits used in these two calibers have the most mass and momentum of any handgun boolits, and at the pressures they operate at, the resistance from swaging a hard cast boolit into the barrel puts a LOT more stress on the barrel and frame than lesser calibers which have no problem using boolits several thousandths over groove diameter.

[Taterhead]

That's interesting data to ponder, Doug. I appreciate your insight. I have a fairly narrow repertoire of cast bullets. I haven't ventured into the big bruiser revolver cartridges.

[waksupi]

Don't keep them near a refrigerator. I seem to gain in diameter from close proximity to mine.

[Taterhead]

Don't keep them near a refrigerator. I seem to gain in diameter from close proximity to mine.

Truth! My belt tells me that work from home has not been good for diameter.

[243winxb]

I let some sized 44s sit for years. Diameter never changed. http://castboolits.gunloads.com/showthread.php?319176-Size-Lube-fresh-cast-boolets/page2

[Taterhead]

I let some sized 44s sit for years. Diameter never changed. http://castboolits.gunloads.com/showthread.php?319176-Size-Lube-fresh-cast-boolets/page2

Thank you for the link!

[Wheelguns 1961]

I have also noticed the larger bullets getting fatter. With my heavy 480 bullets, I usually wait 2-3 weeks before sizing, this has solved the problem for me.

[Taterhead]

I like to size shortly after PC or HT while the alloy is relatively soft.

[blackthorn]

I have also noticed the larger bullets getting fatter. With my heavy 480 bullets, I usually wait 2-3 weeks before sizing, this has solved the problem for me.

So, I have a question:--What happens if you cast, air cool, wait 2-3 weeks, size, oven heat treat and quench right out of the oven? After 2-3 weeks have the bullets grown?