To help the stick problem, have you tried just a touch of lube? Not too much or it will migrate into the mold cavities...but just enough to help the release of the sprue plate. As far as tightening it, tighten it down with a wrench. If you get it too tight though, the sprue plate may slide under it. There is a fine line. I had the same problem with a lyman 4-cavity mold. The bolt on the far side of the mold that the sprue plate slides under to "lock" it in place came loose and was causing the base of the boolits to be funky (because there was a gap between the sprue plate and the top of the blocks.) I tightened it down until it was firmly screwed in and I knew it wouldn't come loose, but then I couldn't get the sprue plate to slide under it. So, what I did was take a thin piece of copper and used it as a spacer to tighten the bolt down on to. This raised it up and still gave me the ability to tightten it down so it wouldn't back out, and my sprue plate slides under it nicely. It takes some trial and error. Remember the sprue plate should slide under it fairly easily. If your bushing is too tight, then it will be too hard to open the sprue plate and you may find you have venting problem. Lyman claims that some venting occurs between the sprue plate and the top of the blocks. Is it true, I would probably think so! Good luck!
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