Having Mold Fill Problem

[Larry Gibson]

Most all "range lead" and COWWs is going to be antimony rich and very tin poor. You answered the question; add tin. Add 2% tin. As to heat; No need to "frost" the bullets. I you use a bottom poor and are filling #1 cavity first the problem is probably the alloy sitting in the spout has cooled. Either raise the temp a bit and/or let a small squirt of alloy out just prior to putting the mould under the spout and cast at the same temp. The alloy is best at 700 - 725 degrees. If you are filling the #1 cavity last then let a large sprue develop on the plate, even if it runs off, with that molten alloy boiling back up out of the cavity.

Also if you are casting set a tempo that keeps the mould temp consistent and the alloy in the spout still hot. If you dump the bullets and then inspect them before closing the sprue plate and casting again the mould will cool a lot as will the alloy in the spout. I suggest when casting that you cast. Inspect the bullets and cull out defects later. That will set up a proper tempo. Although, when warmer and the sprue takes longer to solidify dump the bullets, close the sprue plate, cast then inspect while that sprue is solidifying.

[rintinglen]

^^^I concur. A little tin and cast fast, to paraphrase the Gambler, "You never check your boolits when you're casting at the lead pot, they'll be time enough for checking, when the Castings done."
But I would also thoroughly clean the vent lines on the problematic cavity and, if need be, refreshing them lightly with a knife-edge swiss file. I had a similar problem with a 358-477 4 cavity that had been heavily used and had the vent lines mashed shut.