Aluminum Mold: Does it require a different technique?

[uscra112]

Non-contact "thermometers" are wildly unreliable as far as accuracy goes. Only use for judging relative temps. Don't assume correlation with an immersion type or a contact thermocouple. And that laser is just an aiming aid, it has nothing to do with the actual measurement.

[RG1911]

Weight sorting:
The bullet mold is a "sack" that you are pouring lead in.
You want it full of lead only.
You are looking for bullets at the high end. Not the middle of the distribution. Weigh enough "good" bullets and you should see a skewed distribution.
The few higher than the high end of the skew might have a little bit bigger as dropped diameter due to the blocks not being closed as tight, or a small residual sprue, etc. That's not a common distribution characteristic (hopefully).

If I see it I try adding a little tin.

Excellent information and advice. I should excavate my way to the back of one of the storage units where I have 800-1000 pounds of various pure lead, lead alloys, linotype and some tin and drag some home. The current mix might benefit from a bit more linotype or tin.

Cheers, Richard

[Bazoo]

The bullets you've circled in red, I think you'll find that they shoot just fine. Very minor surface flaws, like a slight wrinkle, or some dross don't affect the bullets unless the very best of accuracy is desired. Dross in the bullets, like it appears you may have on the right bullet in red, is from not leaving a large enough sprue puddle. I can't tell for sure because of the pic, but it looks like dross inclusion. Anyways, some decent looking bullets. Looks like nice sharp bands.

[Maven]

It has probably been said already, but yes, you do use a slightly different technique for Al moulds.

By no. of cavities: If it's a Lee 2 cavity, clean the mould and "lubricate" the pins as per instructions, smoke each cavity with wooden matches or a butane cig. lighter, then begin casting when your pot temp. is 800 deg. F. You can turn the temp. down once you get perfect bullets. If it's an Arsenal or NOE multiple cavity mold, clean and break in according to the instructions, then start by filling only 1 or 2 cavities until you get perfect bullets, then continue until you can fill all cavities and get perfect CB's. You may need to "smoke" the mould if you're not getting perfect CB's.

By brand: I've found Arsenal, LBT (2 cavity only) and NOE moulds need the least attention, e.g., smoking, while the Lee's, both 2 and 6 cavity need more, e.g., deburring and smoking (see Sticky on Leementing).

Temperature: I use a TelTrue brand thermometer and generally cast between 750 - 800 deg. F. You can reduce this once you're getting perfect CB's, regardless of the no. of cavities.

Hope this helps!

[kevin c]

I have only ever used aluminum molds, though I do have a couple brass molds in calibers I don’t really shoot so never got around to using.

My aluminum 8 cav MP molds have an optimal casting temp range that I drop out of or overshoot fairly easily, the first if I slow down too much or it’s cold out, the second if I go too fast. My best boolits in terms of fill out and lack of culls happen with an even light matte frost, so I run hot at 720°.

Most often I preheat in an insulated mold “garage” on a hot plate, and run until I lose the frosting and fill out suffers. That can be anywhere from 20 up to 50 odd fills.

[JoeJames]

Aluminum molds lose heat faster than iron molds. So, this means your casting cadence needs to be a little faster. Another thing to watch is the temp of the steel sprue plate. This will not heat up as fast as the aluminum mold. The hot lead can be cooled passing through the sprue hole, acting just like your mold is not up to temp. Once the sprue plate gets to temp, wrinkles go away and your mold will settle in and start producing good bullets.

Heating the mold on a hot plate with the sprue plate down against the hot plate is the best way to preheat that I have found so far.

Hope this helps!
Sam Sackett

Per "From Ingot to Target" I tried turning my Lee Aluminum mold upside down and sticking the end of the sprue plate into the melt for a short time. Before casting. My problems vanished.

[TurnipEaterDown]

Sprue plate temperature -- I will just pour 3-4 ladles full over the sprue plate on the first cast after filling the cavities (and after warming the mold to start out with). I pour the ladle on the plate enough times such that the molten lead just runs off the plate rather than hardening. Then I know the plate is not going to be an issue. Also warms the mold some more.