Weight-sorting brings up questions...

[selmerfan]

So I'm just now entering a further stage of CDO in my casting/reloading hobby. Decided to start weight-sorting my naked cast boolits. Boolit in question is GB 6 cavity copy of a Lyman 358627. With 50/50 WW/Pb or Lyman #2, the naked boolit weighs in right around 217 gr. My standard for rejection is outside of a 1% deviation, therefore 216-218 gr. boolits are fine. With most of the boolits that are too light to make the grade, a closer visual inspection reveals the problem - rounded base, bands not sharply filled out, etc. BUT - here's what's driving me nuts. About 6 of the boolits look absolutely perfect, picture perfect. But they are 3 gr. lighter that the 217 median! What do you suppose is causing this? Bases are good, no big divot when the sprue was cut, nothing obvious. They look perfect, but they're not. Suggestions? On another note, it's interesting that when the boolits are too heavy, they are quite a bit too heavy, like the mold isn't closed all the way, but no flashing or anything. Just slightly larger in diameter, and that adds us to several gr. heavier in weight. So, I've learned at least one reason I'd get the occasional flyer at 100 and 200 yds with my cast boolits out of the .357 Max Encore barrel - weight variations. Hopefully that will disappear, but who knows, the nut holding the gun still has to do his job!
Selmerfan

[runfiverun]

an air pocket in the boolit.
they are called voids.
nothing out of the ordinary,i once found a 4 lb hole in a 25lb lino ingot.

[Wayne Smith]

... and the letters are in the order they ought to be." Yeah, I love that T-shirt. Runfive's got it right. If you cut those light boolits open you will find voids in them. As you have noticed, lead is dense. You don't need a huge void to make up a couple of grains.

[selmerfan]

A small void was also my theory, but I wanted further corroboration on that. Probably exacerbated by the fact that this mold likes being "swirled". In order to get clean base fill-out I tilt the mold at about 30 degrees towards the pot and pour so that it swirls in the side and keep a good stream on the base for a couple of seconds while the excess pours back into the pot. It takes two ladles to pour the mold this way, but it makes for very nice boolits, and this mold frustrated me for quite a while before I figured that technique out. So I bet I had a little splash over into the next cavity that cooled, then I poured in on it and it didn't quite end up perfect inside, though the outside is great.

[HORNET]

There's also the possibility that the mold wasn't fully up to temperature on a couple of those pours. I had some 321232's that were about 1.3 grain lighter than the main batch and they were very shiny instead of the lightly frosted look of the others. Started saving too soon when restarting after adding alloy and the mold temp hadn't stabilized yet. That second pour cavity filling will do it to you also. On the heavies, make sure that you're not holding the sprue plate handle on that 6 banger when casting. It can bow things and give a lot of size and weight variation. Fairly common problem on here.

[selmerfan]

Mold temp was good - I pre-heat on the hot plate while the melt is going. I figured out the sprue handle trick just last week - don't hold it! Couldn't figure out why i was getting such a variation in diameter!