What am I doing wrong?

[koehlerrk]

OK, got my first Mihec mold... I read up on heat-treating it, so I cleaned it with dish soap and an old toothbrush and lots of hot water, then put it in the oven and heated it to 375, heat soak for 30 minutes, then shut the oven off and let it cool. Repeated this cycle 3 more times, and the brass was noticeably darker each time.

Finally I cleaned it one last time with carb cleaner, bolted the handles to it, lubed it, and brought it up to temp.

I cast bullets for 45 minutes with it, and could not get a single bullet that wasn't wrinkled horribly. They did release nicely though.

Just for kicks I warmed up another mold and it cast beautifully. So, the alloy (isotope lead) works just fine, as always.

Is it not hot enough? Do brass molds need higher melt temps? Does it need more cycling? The obvious one, lube in the cavities, is a non-issue as I always put sprue lube on a q-tip to prevent it from getting in the cavities.

What am I missing? What am I doing wrong? Why is this mold being so difficult?

[longbow]

I would say to preheat the mould more. I find my brass moulds like hot alloy and they like to be run fast to keep the mould temperature up.

I preheat until the sprue plate lube starts to smoke a little and that puts the mould just under the melting temperature of the lead. As I cast the mould cools a little so the sprue puddle takes a few seconds to freeze then I keep up a cadence to keep the mould hot. You can overheat a brass mould though and apparently they can warp so don't overdo the preheating.

I would try that first.

You say you are using isotope lead, is that pure lead? If so a little tin may help with fillout though if it cast well in another mould I think that indicates that the mould is not hot enough.

Another trick I use use is to very slightly break the top edges of the mating mould faces so air will vent under the sprue plate. Most of my moulds get this treatment. I use a diamond home and just barely take the sharp edges off.

My Mihec moulds all cast perfectly but they do like to be run fast and hot.

That's what works for me anyway.

Longbow

[Lon246]

My brass molds seem to like the melt between 700 and 800 deg F.
The melt has small % of tin, antimony and arsenic for water quench hardening.

[koehlerrk]

Isotope lead, if I'm remembering right, is 2% tin, 2% antimony, and it fills all my other molds (aluminum or iron) very well running at 650F.

This is my first brass mold and I was asking because I didn't know why it was wrinkling. Too cold a mold and melt for a brass mold is easy enough to remedy. I will try it and report back.

[RickinTN]

When you've tried everything else smoke the mold lightly with a disposable lighter. Some of my molds, although I don't have any brass, need to be smoked lightly and the wrinkles go away like magic.
Rick

[Maximumbob54]

I feel a bit silly saying this but I've noticed that brass molds seem to have a little black magic in them. I have the exact same problem with one of mine that I cannot seem to solve. I've even allowed it to soak in acetone to see if that would change anything. Wish I could help. I've tried heating the mold, change the alloy, running the furnace at 800, and more. Adding heat did help but they still look miserable. I hope I haven't put something into the brass that I cannot get back out. The rub is that the mold worked fine for a while and now I cannot for the life of me get anything to come out right again.

[RED333]

Here is what I do, get you lead temp to 800*F.
Get your mold temp up with preheat, I use an old lee bottom pour with the rod out of it.
Start casting, as fast as you can, DO NOT LET THE MOLD COOL.
When you puddle takes 2 to 5 sec to get hard, it should be hot enough to cast boolits.
The cool thing about casting is you can recycle bad boolits.
When you are casting good boolits you wont want to stop.
My 10mm/40 cal mold takes 5 to 10 cast cycles to get up to a good temp.

[RobsTV]

You should not need to get the molt above 750.
Try around 700 to 725.

Adjust the molten lead level so that you can place the mold spru across top of pot, and brass mold rests 1/8" above melt. Let it sit that way for 10 to 20 minutes. Cast and if spru puddle stays liquid for more than 10+ seconds, good, it is now hot (too hot). Keep slow pace going so that spru gradually hardens in around 3 to 5 seconds, then speed up to maintain that 3 to 5 second hardness. I have one 2 cavity Mihec mold that need to cool closed for a 15 count before adding lead and repeating, otherwise frosted edges.

[koehlerrk]

Tried it tonight with the melt at 700, mold was hotter than I've done before, and (insert drumroll here) we have success... sorta. Still getting wrinkles on the end cavities, so I bumped the pot up to 725. What a thing of beauty! Pretty little bullets without a single wrinkle anywhere!

As I said in the OP, I figured I was doing something wrong... in this case I wasn't accounting for the heat transfer and higher specific heat of a brass mold. All I had to do was warm her up a bit more. Thanks for the help everyone, much appreciated!

[RED333]

Well now you owe me, O lets say 5000 dollars.
Hanging around here is better than collage.
Congrats and cast away!

[hicard]

You stated that you lubed the mould. My guess is that some of the lube got onto the face/cavities of the mould and that is what caused you the problem. As soon as it all burns off, you will be ok. It would help to wipe off any excess lube before you start up again.

[koehlerrk]

RED, I'll give you 5,000 in Zimbabwe dollars... that's about $0.07 if my math is right.

You're not kidding about this place being an education. I've learned a heckuva lot here over the last few years, it's definitely one of the best places on the whole web.

hicard, normally I'd say maybe... but in my case, no to the lube problem. See, I learned a long time ago from some guys here that the best way to make sure your lube got where you wanted it was to apply said lube with a q-tip. No drip, no runs, and none in the cavities. That's why I figured I was doing something wrong... and I was right.

[RED333]

RED, I'll give you 5,000 in Zimbabwe dollars... that's about $0.07 if my math is right.

You have a deal my friend!

[koehlerrk]

Cast some more with that mold last night... man what a thing of beauty! The bullets practically jump out of the cavities!

Miha, in case you're reading this, thank you for a great mold, I look forward to using it for many years, and while this is my first Mihec mold, it won't be my last.

[RED333]

They do cast VERY WELL, I have a few of his molds and will keep them to pass down.

[super6]

Koehlerrk, Thanks for shareing your experence with the new brass mold, I just got mine and could not wait to cast with it! total failure was the result. I suspected the mold was just not hot enough, I hope you have just confirmed that. Will try again latter today and post back.

[super6]

Hotter mold temp, And better, not perfect but better. The trick that worked the best was taken from a post above, Vent the air that the pour displaced! Just loosened the sprue plate screw and that did the trick.