I'm in the process of switching over from swagged balls to casting my own. Today, I cast 116 .54 caliber balls from a new Lyman single cavity mold.
After they cooled down I weighed every one of those balls on my RCBS scales and I learned something interesting.
91 balls weighed exactly 227.0 grains.
16 balls weighed one to two tenths of a grain lighter. (226.8 - 226.9 grains)
5 balls weighed one to three tenths of a grain heavier. (227.1 -227.3 grains)
That is a spread of five tenths of a grain. or half a grain. That is a heck of a lot better than any of the balls I have purchased, either cast or swagged.
However, I also had 4 balls which weighed 231.2 grains. 4.2 grains heavier than the majority (227.0 grains)
Now I understand how an air pocket inside a cast ball will make that ball lighter than the others. But it wasn't making sense to me what caused those 4 balls to be that much heavier. Were those heavy balls the only ones that didn't have an air pocket? What in the heck was I doing wrong to get that many light balls? I worried over this for a couple of hours then walked away from it.
Latter, I came back and took a closer look at those heavy balls. I noticed that the mold line (or seam) appeared to be more pronounced on them. When I ran my fingernail over them I could feel those lines. On the other balls I could see a faint line but I could not feel it with my fingernail.
Thinking on that, I concluded that some of the hot lead must have gotten between the mold half's. But that tiny bit of extra lead could not amount to 4.2 grains.
What the heck???
Then the little light bulb came on. In order for lead to leak between the mold half's I must not have had the mold completely closed. If that were the case, wouldn't the ball be just a bit larger than the rest?
So, out came the dial caliper. Those four heavy balls measured .538 and the others measured exactly .532
I think I found it out!
So, what I learned today;
1. The balls I'm casting are much more consistent in size and weight than any I can buy.
2. Be sure to close the mold tightly in the future.
Some of my friends think I take this stuff way too seriously. (They may be right about that, but they aren't beating me in the shooting matches.)
Those four heavy balls went back into the lead pot. 91 of them went into a box marked "matched 227.0 grains" these will be used for load development and match shooting. The others went into a leather bag for off-hand shooting at gongs.