I've been enjoying my efforts at trying to creat the perfect Soft-nose bullet, utilizing the info. provided by BruceB and others. Definately making progress here, and am now at the testing stage of these specialized hunting bullets. However, during the casting process there was one recurring problem that accounted for 100% of all my rejects; I experienced poor fillout of the bullet bases, some so bad that they simply could not accept a gas-check! Since I do not have this problem when casting normally, I could only assume it has something to do with the extra heat and cooling time involved in this process.
In attempting to correct this, I decided to cool the mold with a damp towel only from the mold base, and leave the top or sprue plate area air cooled only. I felt that because of the high mold heat involved, the draw down that occurs with normal mold temperatures and sprue formation was not happening and that the bases of the bullet were being "starved" by a sprue that had hardened prematurely. Cooling the mold base only helped, but the problem of poor bullet base fill-out though improved, still existed. Here again, I'm thinking that the time involved in cooling down the bullet results in a sprue hardening prematurely whether cooled by air or a damp cloth.
Other efforts at correcting this condition have included increasing the tin content, and air cooling only before dropping the bullet, but these have not helped. Perhaps I just really don't understand "draw down", or am I looking in the wrong place for a solution? Any suggestions?
Thanks,
BrushBuster