the hot alloy keeps hitting that spot.
long skinny bullets do best for me if i line up the hole and shoot the alloy in straight to the bottom.
I have a Lyman 314299 mold that makes the a nice bullet, .302 on the nose, they are sized and ready to load, so do not recall what they drop at for body dia.
One thing that does happen is I get a frosted spot forward of the front driving band that extends +/- 1/4" up the nose, that is slightly sunken.
What are/is the cause(s) of this and remedy(s). Not sure if the mold is too hot, to cold, the melt to hot or cold.
If I may pontificate on this a bit, I hope fiver doesn't mind?
I assume all of us that have cast long skinny bullets have had this issue, I know I sure have.
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A few years back, I came to the conclusion, that this happens when there is a cold spot, I figured it was block design...groove for handle or holes for alignment pins, where a part of the mold cools faster because of metal density, ...and the long skinny bullets were just more susceptible to a mold with a cold spot. With these molds, I usually have good casts for a while, maybe 15 or 20 pours, then I start to get the shrunken spot on side of nose as Michael describes. My solution was to stop casting, put the mold back into the mold oven to have the mold temp even out throughout the blocks. This has seemingly solved the problem...temporarily, until it starts doing it again in 15 pours, LOL.
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Now Fiver's comment has me rethinking the situation. Not a cold spot, but a hot spot. Fresh hot alloy hitting the same spot during the pour, due to pour angle, from hitting edge of sprue hole or whatever, sprue hole thing makes most sense. The hot spot keeps the alloy in that little area from freezing with the rest of the bullet. That gives that spot the opportunity to shrink, since it can't pull alloy from the sprue puddle during the freezing in that little area.
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Again, I hope you all don't mind my pontificating, because I need to reconcile the situation in my head and typing it all out will likely help me remember it.