Last fall I made a new batch of alloy. About 400 lbs or so. While I was working out of state the other Mainiacs foolishly allowed the state to outlaw lead wheel weights so this batch was something I made using pure lead from phone company splice boxes, old plumbing and flashing scraps, combined with antimony powder bought on this site and some pewter accumulated over the years, filled out with about 200 lbs of smelted down window sash weights from a 200 yr old home I tore down at work. By my primitive calculations I should have been somewhere around 95/3/2. The issue is a problem I haven't seen before: Voids at, (under) the sprue. I was using molds I've had for years, #68 H&G and 230 BDACP for 160 lbs or so,(several hundred thousand boolits cast in them previously), with the exception of a new 147 grain 9mm mold, (maybe 20 lbs cast). Same Master Caster I've used for years, same temp, same technique and timing, boolits and sprues appeared completely normal while casting, although maybe not as much visible shrinkage on the sprues down into the mold, (This is a little hard to judge on a master caster as you don't get a good eye on it until you move the mold out from under the spouts.) The voids are more or less centered in the base under the sprue. Larger and more obvious on the 45's, smaller and less obvious on the 9mms. The boolits all look great, except for the 5% that show some level of void at the sprue. The rest of them weigh as consistently as usual, so I don't think this is random voids. I'm thinking this has to be an alloy issue involved with the fill/cooling at the sprue?
5% is not a huge issue, it's just one more thing I have to look at individually which is a PITA when working in bulk.
Any opinions on this? I have another 400 lbs or so of this material and I'd like to get a clue before making more alloy.