Air bubble?

[jcw1970]

I'm casting a lyman 280473 and i've cleaned it, made sure the vent lines are clean, i'm up to temp but i keep getting these spots on my boolits. Always in the same spot and it happens on both cavities but not all the time. Are they air bubles? Any clues?

[Ben]

Possible causes ( in the order that I'd expect to find the answer )

(1) Mold still has traces of oil in it.
(2) Mold needs to be sooted with a Bic lighter.
(3) Venting problems ( could be solved by beagling with a single ply of foil tape )
(4) Alloy not hot enough
( 5) Mold not hot enough
( 6) Additional Tin needed in your alloy

[DLCTEX]

Most likely, cold mold. Second, oil contamination. After that, the rest of what Ben said.