Mold cavity sticking weirdness

[texassako]

I have a new to me dual cavity Modern Bond mold that sticks a bullet in one cavity in one block. OK, been there and done that with other old molds but it has been a stubborn one trying to fix(removed burrs, lapped). After the third time thinking it was cured and sticking again I tried casting each cavity by itself since they are different designs anyway. No sticking in either cavity; so I treated it like a single cavity and cast for a while. I have never run into a mold where a sticking cavity is 'cured' by only casting in that cavity. Thoughts?

[bhn22]

Try letting the mould cool for a few more seconds before opening. Whatever the issue is, it appears to be related to the temperature of the mould.

[Yodogsandman]

Is the mass of the different boolit styles much different from each other, like say a 100gr and a 200gr. The mold could be having trouble maintaining the proper temperature on both sides at the same time for optimal casting. It would be hard to adjust your cadence to maintain that heat on both sides without affecting one or the other. Just continue to cast one cavity per session, if that's working for you.

[texassako]

When you lapped the cavity to remove the burrs, likely you removed the bluing. This left a clean white surface that could allow the lead to solder onto. By casting with one cavity only, the other cavity had a chance to oxidize, so much more difficult to solder to.

What really bugged me was an LBT mold (aluminum) that would stick, and was obviously soldered at the split lines.

Excellent suggestion, except it stuck before I lapped and will stick on command if I cast both at any time in a casting session. I am going to put some cold blue in it anyway just in case after one more lapping session. It had a ding on the cavity edge when it came to me; so I knew it had a problem right off the bat. It does not seem to be sticking there after working on that spot before I even fired up the pot.

Try letting the mould cool for a few more seconds before opening. Whatever the issue is, it appears to be related to the temperature of the mould.

Casting for a while I did figure out that temperature alters the stickiness. If I cut the sprue and drop as soon a possible, it sticks less.

Is the mass of the different boolit styles much different from each other, like say a 100gr and a 200gr. The mold could be having trouble maintaining the proper temperature on both sides at the same time for optimal casting. It would be hard to adjust your cadence to maintain that heat on both sides without affecting one or the other. Just continue to cast one cavity per session, if that's working for you.

The weight differential is ~150 gr in one cavity and ~190 in the other, but they are fairly long .30 caliber pointy designs. I am going to see if one more session of careful lapping will cure it (don't want it any bigger), but I may just need to treat it as two different single cavities in one block.

[bhn22]

How are your antimony and tin percentages in your alloy? Have you tried casting with pure lead to see if that sticks in the mould? About 3% tin & 3% antimony is all an alloy needs in most cases. Higher antimony could result is slightly larger bullets. Not a huge difference, but it could be just enough.

[texassako]

The current alloy in the pot is COWW + 2% tin.