I just finally gave in and decided to cast for 9mm and 40S&W after avoiding it forever due to the usual cautions about it being more difficult than working with lower pressure rounds. I figured since I now cast for several old millitary cartridges in additon to all the revolver cartridges I shoot, plus .45 ACP, I may have passed the point in the learning curve where I should not let this issue slow me down. I read a good bit here and I know about the importance of fit, and proper case mouth expansion etc. so figured I'd give it a go, starting with a couple of Lee 6 cavity molds.
Both arrived with what I thought was pretty amazing fit and finish (look at those nice shiny cavities) for an inexpensive mold but both also had an issue that looks really odd to me. I've only cleaned up the burrs on the cavities and scrubbed the molds but did not yet have a chance to cast with them. The oddity is that there are three passes across the mold faces with a mill and the one in the middle clearly is deeper than the other two. It felt like maybe a thou or two and while it was tough to measure properly due to the position, it mic'd out at about .0015" or so. That adds up to .003" gap or so when the two are put together. I looked into the cavities with the mold halves together, using magnification, and I am afraid I am going to look forward to feathered bullets. Could this be to allow for perhaps greater expansion near the center of the mold (because the mold is thinner there due to the grooves for the handle jaws and will become hotter in that area)? Or....is this an odd method of venting...or just a mistake? In the past, with other molds where I maybe had a lead booger on a mold face, a gap like that could end up accounting for feathering.
I have another Lee 6-cavity somewhere and I need to hunt it up to see what it looks like. I appreciate any wisdom the group can offer!
Paul