FWIW the Lee and RCBS RB moulds have a tangential sprue cut. Sometimes in the same nominal diameter they both have a + or- cut if you check different moulds. Production tolerances I guess. If you have a choice buying, open the mould and look.
The Lyman has a cylindrical tube of casting metal that is cut off by the sprue plate, also + or- to the ball surface. The Tanner mould has the tube also that you must cut off to minimize and deal with although I think the roundness is a measurable bit better than the named competition, but that is offset by production time.
You can put a couple of hundred of your RB(depending upon total weight) in the smallest Thumler's tumbler for about 4 hours and make the well trimmed upstanding sprue tubes disappear, and the roundness measurably improves also, especially on your best tangential cut ball, depending upon how far it was out to start with. I'm talking LEAD here, not an alloy ball. Nothing but the RB to be tumbled is needed in the tumbler, NOT A VIBRATORY CASE CLEANER. Riding RB around in my car trunk only produced decreased gas mileage in my experience and made little measurable difference.
After my fooling around on this question for some time, I now tumble all RB I cast, send the tall sprue tube moulds down the road for the guys of the sprue up ritual, cherish the right on nominal roundness moulds, and poke down the barrel without regards to orientation, the RB I make.
Lon
