Undersized Casts

[JFriis]

Hello all, sorry to bother with such a question as I am sure it has been covered, but I cant seem to find an answer.
To the point, My Lee mold is casting undersized and underweight with an unknown alloy (ingots made by someone else). The mold in question is designed for 9mm or .380 and is supposed to be a .356 diameter. Unfortunately, they cast at .354.

Is it possible that my alloy is too blame? I know that different percentages of tin can change the size and amount of shrinkage, but I didnt think they would be that much smaller. Also, these bullets are supposed to be 121 grains and weigh in the 114-115 grain range.

[45nut]

Is it possible that my alloy is too blame?

In a word, yes. I would seek out a known alloy to try. Pure lead vs Linotype alloys will be wide apart.
Also try the alloy in a different mold to see where it stands.

[JFriis]

In a word, yes. I would seek out a known alloy to try. Pure lead vs Linotype alloys will be wide apart.
Also try the alloy in a different mold to see where it stands.

I meant to mention that the same alloy in multiple .452 molds cast at .452 as expected. I figure the problem to be an undersized Lee mold based on that, but I am unsure. :???:
All casts done as of yet are 5-7% underweight per expected weight.

[Ben]

A simple test is to heat your current alloy and pour it ALL into an ingot mold.

Now start over with a completely new alloy...........

Refill your pot with straight WW's and pour another 20 - 30 bullets .

When your mold gets up to the proper temp. , mike them & compare notes, and report back to us with your results.

Ben

[nscob]

Im having opposite problem.Mine are .001 to .003 over size and as much as 10 g over weight. The main thing is they wont chamber in autos.

[JFriis]

Had a chance to work on this problem a little this weekend.
Drained all the unkown alloy as suggested and melted some pure lead that I bought just for this experiment.

Boolits still measure at .354 and are a right at the listed/expected weight.

[clintsfolly]

send it back to lee with a note of your findings clint