Shrinkage

[lead chucker]

I have some 308 bullets water dropped and air cooled. When I take the bore riding end and put it in the end of the barrel the water dropped ones seem a little looser than the air cooled ones. Does the water dropped bullets shrink that much. Has any one noticed a difference in size between water dropped and air cooled?

[youngda9]

http://i202.photobucket.com/albums/aa200/Klink_album/seinfeld_shrinkage.jpg

[runfiverun]

i have seen boolits grow a little in a weeks time
i have seen them have spring back after sizing too.
i'm thiinking you had your alloy temp up a little higher this time,or were running the mold a bit hotter.
that'll make some smaller boolits.
and a thousandths of an inch makes a difference in what we do.

[stubshaft]

I have cast boolits and cooled them by water dropping and air cooling at the same time (to get different BHN) and have not observed any difference in diameter.

[pipehand]

Are you checking the bore riding diameter before or after lubeing and sizing? Useta have a bad problem with noses getting bumped up in the in and out sizers(Saeco, RCBS, Lyman) but not with the Star. The softer air cooled boolits may bump the noses easier than the water dropped.

[runfiverun]

I have cast boolits and cooled them by water dropping and air cooling at the same time (to get different BHN) and have not observed any difference in diameter.

when things are done the same way you won't.
if however you increase the mold temp it can make the cavity shrink [it makes the metal swell up causing the hole to get smaller]
manipulating the alloy and mold can make a world of difference between a useable
sized boolit and undersized one.
a trick to learn is lapping, doing it to a hot mold is much more effective..

[Rockchucker]

when things are done the same way you won't.
if however you increase the mold temp it can make the cavity shrink [it makes the metal swell up causing the hole to get smaller]
manipulating the alloy and mold can make a world of difference between a useable
sized boolit and undersized one.
a trick to learn is lapping, doing it to a hot mold is much more effective..

I'm fixen to go out to the shop and lap one of my &%$#@! Lyman molds, Never thought of heating the mold up first. It makes perfit sense though, thanks for the tip.

[Mal Paso]

if however you increase the mold temp it can make the cavity shrink [it makes the metal swell up causing the hole to get smaller]


Actually the cavity gets larger as temperature goes up. The Whole Thing Expands. That's how we install friction fit gears. Heat them in an oven to 450 and they slide onto the cold shaft. The amount of expansion on a 12" gear can amount to quite a few thousandths, in a .5 inch cavity not so much.

[runfiverun]

that's how we get stuff apart too, heat it and let it expand. then coolit quickly to shrink it.
metal expands in all directions though..
i learned the heat lapping from bruce at brp molds,and from 44 man.
try running your alloy cooler like 625 with a mold that's just warm enough to make good boolits. then measure them against what you normally do.

[303Guy]

Metal can only expand outward. But what happens in a hotter mold is the casting doesn't quench so fast so the casting ends up smaller. With a cooler mold the shell of the casting solidifies while the centre is still molten and as it contracts the molten pool from the sprue fills the core. Well, the same happens in a hotter mold but less so.

[Larry Gibson]

I have found, in some instances, when casting "hot" that the WQ'd bullets will be of smaller diameter tha when AC'd. However, after a couple weeks the AC'd ones are close to the same diameter. Not a lot of difference but measureable.

Larry Gibson