Trouble with MP mold

[jordanka16]

I just got my first MP mold, and first hollowpoint mold, and am having a bit of trouble.

2 cavities give me bullets like on the right, perfectly filled out and crisp, the other 2 give me bullet like in the left, rounded and occasionally with wrinkles, no matter what. I have my RCBS melter cranked to 840, I preheated on a hot plate until the lube smokea, and the rounded bullets are even slightly frosted, but still no luck.

I cleaned the mold before I used it, but I'm going to totally disassemble it and do it again, but can anyone think of what might else do this? This is my first brass mold and they behave very differently.

 

[Ben]

Your alloy seems hot enough but that doesn't mean that your mould is hot enough.
Have you cast with it fast enough to make the bullets " frost " yet ?
If so, you had your mould plenty hot enough for good bullets.
You may have a venting problem.
You might loosen the sprue plate some and try it all again.
A light coat of carbon from a butane cig. lighter will often times help with fill out.

Ben

 

[jordanka16]

Your alloy seems hot enough but that doesn't mean that your mould is hot enough.
Have you cast with it fast enough to make the bullets " frost " yet ?
If so, you had your mould plenty hot enough for good bullets.
You may have a venting problem.
You might loosen the sprue plate some and try it all again.
A light coat of carbon from a butane cig. lighter will often times help with fill out.

Ben

Those pictures are after about 30 minutes of casting, none of the bullets come out completely frosty like I get with aluminum molds.

I preheated on a hotplate and within a couple casts I was getting perfect fillout on the first two cavities, but the 2 closest to the sprue plate screw were the trouble ones, I'll try running it looser but it sure wasn't tight.

I took a picture of the cavities, there's some lead speckled on the edges, but that hasn't been an issue before, plus it's on all the cavities, not just the bad ones.

 

[RBHarter]

Yeah I could tell you about the wonder of the MP brass mould ....... 462-420 HB/PB .......it's a good thing it was a door prize and I'm as stubborn as a granite boulder and as patient as the creek wearing it down to dust . Otherwise I'd have sent the thing away loooong before I got good bullets .

I did wash and heat cycle thing exactly as recommended ...... 3 times . 11 casting sessions over 2 months casting up 7-10# of junk every time . I pre heated sprue up and sprue down , closed tight , slightly open , always with the hot plate tent/box . I dipped the corner , floated the base , messed with temps , had a Shaman smudge the casting area while he was doing the house and shop .

Then it happened just all of the sudden for absolutely no reason whatsoever, boom , 5# of perfect bullets . Plain bases at 460-417 and HB at 460-380 within 1.2 gr for the whole batch .

The secret was finally getting the oxide patina on the mould blocks when that happened all of the failure to fill , weird heat distribution stuff with pulled round over heat on one side and cold wrinkles on the other side , round bases etc all stopped . The only thing I have a problem with now is getting the blocks too hot .

I lived in the desert land of what's rust then . I mean you almost can't make bare steel rust in less than 6 months even if it gets rained on . So you can imagine what atmospheric brass patina has to go through to happen .

Be patient try again . When it hits the minimum limit it will let you know .

 

[CWLONGSHOT]

This isnt uncommon. Its because folks dont want hot handles so dont get the blocks closest to handles hot enough. BUT there is also more metal mass there so it compounds the issue.
But Id bet its simply heat and ya aint getting that mold hot!

I run my hot plate @ "1"! But I start it when I start the pot and turn the mold over at least once before starting ta cast. I edit very little from my videos. So when ya see me start, that is how that mold runs. Ill show if there is issues. I had far more issues before the hot plate. But I suspected them to be heat and put the mold back on top Of the pot to warm.

I know its frustrating and hard sometime to hear something you dont feel to be your issue.

Good Luck,
CW

 

[358156 hp]

It gets easier as it goes, sometimes the issues don't make any sense at all, but it will eventually work out. I hated my mould at first too. My solution was to break it down again, and clean everything with Bar Keepers Friend, followed by another round with blue Dawn dish soap followed by a thorough rinse and about an hour in a low oven to dry completely. This seemed to have eliminated any possibility of residual cutting oils. Then by chance I left it sitting out for awhile before I was willing to even look at it again. It did tarnish a bit but it worked perfectly when I tried it again, and I did overheat it a mite the first time out. So I bought another one, then another. I was so accustomed to working with iron moulds that I treated the brass ones the same way with cleaning, lubrication, and rust prevention. That may have been the actual issue all along.

 

[Bret4207]

My sole brass mould is a truly ancient Yankee. Casts like a dream! I agree with the tarnish idea. I don't know if there are any ways to encourage tarnish on brass, but it comes down to the same issue we have with bare steel moulds not acting like one that is blue from heating. At least that might be part of the problem. The other part likely mould heat vs pot heat. Yeah, you can run the pot at zillion degrees, but how hot is the mould? Uneven frosting sounds like you're shy of where you may need to be until the mould straightens itself out.

FWIW- IME I have never had a mould of any material that didn't like being HOT! Some demand being far hotter than others, some are not so picky, but none of them like to run cool. When you find yourself getting slightly impatient for the sprue to cool or you start getting bent bullets after you drop them, that's usually when you make the very nicest castings.

 

[Spindrift]

I have many MP brass HP moulds. They all recieve the same preparation before I start casting with them. I clean them with acetone, then run them through a few heat cycles. Some of them started dropping very nice bullets quite rapidly. Others stubbornly refused to make good bullets for several casting sessions.
I think patience is the key here. The mould will come around, eventually. And when they do.... wow!
Good luck!

 

[Ian]

Mould too cold because you're not casting fast enough. Period.

 

[Rick]

Your pot temp is way too high and your mold temp is way too cool. Brass absorbs heat much slower than iron and far far slower than aluminum. Pot temp does not relate to mold temp, the pot at 700-725 degrees is nearly 300 degrees above a good mold casting temp and will keep any mold up to a good casting temp.

Almost everyone that is accustomed to casting with aluminum or iron molds has problems when first using brass. It is a learning curve. Drop your pot temp to a reasonable 725 and cast faster, don't look at it as pouring alloy into the mold, look at as pouring heat into the mold. Don't inspect the bullets while casting, close the mold and refill quickly, keep going. Brass also gives up it's heat slower than iron or aluminum so once you do get the mold properly heat soaked you can find a good casting rhythm and you will be amazed at the bullets that fall out of that mold. That's the key here, a properly "heat soaked" mold.

 

[Brother_Love]

Your pot temp is way too high and your mold temp is way too cool. Brass absorbs heat much slower than iron and far far slower than aluminum. Pot temp does not relate to mold temp, the pot at 700-725 degrees is nearly 300 degrees above a good mold casting temp and will keep any mold up to a good casting temp.

Almost everyone that is accustomed to casting with aluminum or iron molds has problems when first using brass. It is a learning curve. Drop your pot temp to a reasonable 725 and cast faster, don't look at it as pouring alloy into the mold, look at as pouring heat into the mold. Don't inspect the bullets while casting, close the mold and refill quickly, keep going. Brass also gives up it's heat slower than iron or aluminum so once you do get the mold properly heat soaked you can find a good casting rhythm and you will be amazed at the bullet that fall out of that mold. That's the key here, a properly "heat soaked" mold.

What he said^. I have 2 MP molds that cast beautiful bullets but they have to start HOT. I cast with lead at 725 and turn hot plate all the way up.

 

[jordanka16]

Seems like the common theme is oxidizing the mold, and heat. I cleaned it real good again and I'll cycle it a few times to see if that helps.

I preheated the mold on the hot plate but my fear was getting it too hot and warping it, I've read that is a flaw of brass molds. That's why I had my alloy so hot, with aluminum molds the alloy heats it up, usually too much so I have to slow down.

I don't know if I said it but those bullets are after 30 minutes of casting as fast as I can, with the temp cranked in an effort to heat the mold up, and that's after a preheat until the sprue plate lube smokes.

 

[Ian]

don't know if I said it but those bullets are after 30 minutes of casting as fast as I can, with the temp cranked in an effort to heat the mold up, and that's after a preheat until the sprue plate lube smokes.

Practice more, you're not cycling the mould fast enough. The photos clearly show bullets cast from a cold mould. Four pours a minute for five minutes straight will fix it, get yourself an analog wall clock with a second hand and time the pours. If you're lollygagging along you can cast all day and never get the mould hot enough to fill out. Another dead giveaway that your mould is too cold is the little dip on the bullet nose where the alloy, even under pressure, didn't fill out around the HP pin. Read THIS: https://www.artfulbullet.com/index.php?threads/tale-of-three-bullets.5190/

Now, if you get lightly frosted bullets that STILL have rounded bands, it's time to look at venting. I see some lead specks plugging vent lines in the lube groove area, and ALL MP moulds have the vent lines on the right side of the cavity (looking at the face) plugged by metal smeared by the cherry. However, the opposite side will be clear and that is usually sufficient to vent the mould. You can also try mixing up the order in which you fill the cavities, i.e. start from the sprue plate end or pour the most stubborn hole first.

And for heaven's sake turn your alloy temperature down to at least 750. Pouring too hot can cause a host of other problems you haven't even gotten to yet.

 

[STIHL]

Heat, most all of my issues are heat related, other than old smooth ideal molds, that's the topic of a different conversation.
Hot plates are good, but only if you have something covering the molds to help hold the heat into the mold, and even then they may not be hot enough. I run my alloy around 725-775. Still have the occasional mold that takes 5-10-20 pours to get heat soaked, once it does then its good to go. The oxidation makes sense to me too.

 

[JWFilips]

I got rid of my MP mould after one month ( But I was an inexperienced caster back then!) I found out afterwards that Liquid cold gun blueing
patinatizes the cavities on brass moulds and is safe. I agree with most everyone above....heck they are the folks that thought me how to cast well so they speak words of wisdom....One thing I would be interested in knowing is which way do you fill the mould ...front to back or back to front...I would venture that if you switch directions the other 2 cavities will be the good ones It has to do with getting the 4 cavity mould fully up to temperature in all 4 cavities

 

[jordanka16]

I will heat the mold up some more, I'll try heating it and pouring, then heating it more if I get poor results.

I tried pouring any way I could, front to back or back to front, same results. Always the same 2 cavities not working. The other 2 gave good bullets no matter what.

 

[Rick]

I pre-heat on a hot plate set at 400 degrees. Still takes a good 10 plus quick pours to properly "heat soak" the mold. I have never once heat cycled a mold before casting with it, long before I read of such a thing on these forums I was getting good bullets with a properly cleaned, properly heat soaked mold. If it ain't broke don't fix it. Never once have I watched a clock or anything else to open the mold or refill. Would probably be in a straight jacket and never cast again if I had to do that. Works for some I reckon but it's not for me.

The big secret that many struggle with to good bullets with minimal weight variation is mold temperature. That's it. Mold temperature. It is not alloy temp. A properly heat soaked mold with the alloy only hot enough to keep it heat soaked. That is not hard to do but it is a learning curve just like anything worth doing well.

As a side note you can get frosted bullets from a cold mold if the pot temp is too high. Frosted is not what your looking for. Perfectly filled out bullets of consistent weight is what the correct casting rhythm with properly heat soaked mold will give you. Practice and time will get you there. I doubt there is anything wrong with that MP mold. Any lead spots on the edge of the cavities can easily be wiped off a hot mold with a piece of leather such as heavy work gloves. If needed lightly play a propane torch on the spots until they melt, then wipe off.

 

[Ian]

Never once have I watched a clock or anything else to open the mold or refill. Would probably be in a straight jacket and never cast again if I had to do that. Works for some I reckon but it's not for me.

It's only a universal troubleshooting reference. I can't count the number of people having this exact problem come to these boards and tell you "oh, yeah, I was casting FAST" and "I'm SURE the mould was hot", then they time it and discover they were barely managing 1.5 pours per minute from their enormous, brass, hollow-point mould and if they had a temp probe they'd find the blocks running 250⁰ when they need to be closer to 400. It's a learning curve, that's all.

By the way, the cavities that WERE filling out well were still too cool, you see the faintest rounded edges and if that is the same alloy that frosts in a hot aluminum mould, this one was definitely too cool.

 

[Ian]

p.s. I have cast with that exact mould (borrowed, still have it) and I can tell you you'd better hustle to keep not only the blocks hot, but the pins hot too or you'll get smiley faces on the mouths and big bubble voids down in the HP cavities. I run straight sticky weights at about 740⁰F.

 

[Bret4207]

Are you using a ladle as God and nature intended or one of those bottom pour monstrosities? Are you letting a generous amount of alloy run over the sprue plate? It all helps get the mould up to temp. I've seen some videos of guys that were self-proclaimed experts trying cast and they didn't leave enough of a puddle to say so. Be generous with the alloy. It'll go back into the pot after it serves it's purpose of heating up the mould.