How to run an 8 cavity aluminum mold

[Wm Cook]

I’m thinking about getting an 8 cavity aluminum 9mm mold from MP but I’m worried about difficulties in getting consistent quality bullets out of that long of a mold.

I’ve just never run an aluminum gang mold that big and most of my world has been bolt action long guns, single or double cavity iron or brass molds and casting for match accuracy.

If anyone has had experience or tips they could share I’d appreciate it. Kind of feeling like a rookie on this project. Bill C.

[Hick]

Don't know anything about such a large mold--but I can offer one observation. I use single, double and triple cavity molds, and have noticed that I cannot make double the bullets with a double in the time it takes to make them in a single. In other words, the extra time spent filling more cavities partially offsets the savings in time of more cavities. So-- unless you really have a need to make huge quantities, you are better off with fewer cavities. Said differently, there may be an optimum where you get your best results because it is easier to consistently fill the cavities even though it takes more loads of the mold.

[kevin c]

I use MP aluminum 8 bangers to produce a lot of boolits quickly, so here’re some observations based on personal experience.

In no particular order:

Miha’s high quality molds have pretty consistent cavities. Not as consistent as a single cavity mold, but we’re talking semiauto pistol boolits, where 2” groups at 25 yards are about as good as you can get. The right loads topped with an MP cast are more accurate than I can shoot.

A bottom pour with a mold guide will make you more consistent and spare your muscles from the shoulders down to the hands. Mount the pot high enough that you can see the spout and the cavity under it.

Preheat ingots on the top of the pot, as many as is practical and safe; it is surprising how fast you’ll go through alloy even with a large capacity pot. Better, and which also minimizes temp fluctuations and downtime, is to mount a feeder pot.

Putting the mold on a hot plate is an easier way to evenly heat those long blocks than dipping a corner into the melt or casting and discarding several pours. I use a K type thermocouple in a cavity and go for around 400°F, higher in cold weather.

I find Miha’s molds best cast 95-3-2 alloy when run hot. The bullets are just about flawless with very few culls when dropped with just a very light matte frost on them. For cool weather outdoor casting, PID controlled pots at 730° to 740° work best, but this rides close to heavy frosting, excess shrinkage with weight variation, and also lead smearing and sprue pull-out divots, so for cooling you may have to adjust cadence or open the mold a bit longer. Some folks cool the mold on a damp rag or sponge. If you do this, make sure the ferrous fittings on the mold are well oiled, both the exterior and interior surfaces, or you’ll be dealing with rust.

Alternating pulling/pushing the mold under the spout helps to keep the end cavities more even temperature wise.

Be sure that the sprue plate is fully closed against the stop for each pour. If the sprue hardens with the plate holes offset from the cavities, even by a little, the cam loses its mechanical advantage and it’ll be almost impossible to cut the sprue. MP 8 cav molds have wave washers on the pivot and stop bolts to hold the plate closed during normal handling, so you shouldn’t need to hold the plate closed with the cam handle.

I use the HiTek bonded mold release. Regardless, a little extra persuasion helps the bullets drop more easily (a stubborn boolit really messes up the cadence), so I use a lead weighted rawhide mallet.

The long sprue plate is steel and has that handle hanging off the free end. With the plate swung open, there’s a lot of weight and leverage putting uneven pressure on the block around the pivot bolt, and it’s easy to get semicircular scoring on there. To minimize that I support the handle and plate on the landing area when dumping the casts. I also use an aluminum anti seize and make sure the bolt is neither too loose nor too tight.

All the bolts (block and cam) loosen as they heat up, so an 10 mm socket is handy (but DO NOT over tighten). MP provides a hex key to tighten the set screws, though they also loosen up. A divot or flat in the bolt for the set screw to bear against helps, but I always had trouble getting that permanent (at least until you get a replacement bolt) fix just right.

All three wooden handles loosen over time. You can tap them in again, but, between drying out and scorching, they’ll loosen back up quickly. JB weld doesn’t last. Consider pinning the handles.

In the groove and using dual pots (feeder over casting bottom pour) I usually produced around 800 good boolits an hour with few culls. A session of 1-2 hours, a break and maybe another session was a good day’s work for this senior.

That’s all I can think of for now. Good luck!

Second edit: the proper socket is a 10mm, not 11mm. My apologies

[farmerjim]

I use two, 4 or 6 cavity molds at a time with a 25 pound bottom pour pot. I keep a pot full of almost melting ingots on a hotplate.
You can go faster with 2 molds than you can with 1 long because you don't have to wait for the mold to cool.

[Wm Cook]

Kevin your answer should be kept as a sticky on how to use large multiple cavity mold.

I was so concerned about maintaining an even mold temperature that I forgot you had to feed the darn thing. Plus I didn't give near enough consideration to the normal wear and tear on a mold that big.

Preheating ingots is a practical suggestion for all casters even for me when I'm casting with a single cavity mold. Rather than a 15 minute pause in getting fresh alloy up to temp you can be back casting in half the time. There was high value in all the details you took the time to explain and I greatly appreciated your help. I second your opinion of MP molds. I only have four but they run smooth and consistent.

I think there's a very practical place for 8 cavity molds. But it would be foolhardy jumping into it without serious considering given to keeping it fed and keeping it maintained. Thanks again, Bill C.

[dannyd]

Just got a MP 8:cavity mould the thing is great to use; fill the pot with lead and away you go. Makes a lot of bullets.

[Intel6]

I have a MiHa 8 cavity bullet for making smooth sided 160 gr RN bullets for use in my 9mm competition revolver. I had never used an 8 cavity before but after proper break in all I do is heat it up on a hot plate and start casting. The bullets jump out of the mould and they pile up quickly. I do use a mould guide and make sure I keep my operating temps (mould and alloy) steady.


Mould in use




Bullets coated in both PC and HiTek sized and also loaded in cases specifically for my revolver in the center and the load on the right is a shorter LOA for shooting in autos.

[Targa]

I am in no way some master casting guru and if I can get them to work anyone can. Buy the thing, once up to temp it will rain bullets ready for sizing. I have the 8 cav 124 grain rnfp for 9mm and 8 cav 158 grain swc.

[Wm Cook]

To DannyD, Intel6, Targa; Kevin mentioned “ With the plate swung open, there’s a lot of weight and leverage putting uneven pressure on the block around the pivot bolt, and it’s easy to get semicircular scoring on there. ”

Do you do the normal 2 stroke lube to keep from scoring the mold face? Bill C.

[Intel6]

Yes, that is what I have been using since I started getting small bottles of it when I first started buying NOE molds.

[bruce381]

Start mold hot I use a hot plate put it on when Pot is on also made a PID pot is set at 725. MP molds are very nice i just cleaned with comet and real good rinse and works great, MP said run his mold hot.

[mvintx]

What kind of pot do you guys use to preheat your ingots?

[Targa]

Although not a bad idea, I have never preheated my ingots. I just drop them in the pot, turn it on and let them melt.

[toallmy]

Dropping a cold damp ingot in a hot pot could make bad things happen ....

[kevin c]

I edited my long post (#3) to correct the MP mold socket size to 10mm.

I use the CastBoolits/RedneckGold ingot molds sold by Lakehouse2012: they’re long enough to span the top of the Lee 4-20 that I use as a feeder pot. I usually put one or two there, but three will fit if stood on edge between the screws around the lip. They’ll get hot enough that I use pliers to put them into the melt.

Cold or empty pot: I just stick the ingots in straight from storage. Not worrying about a visit from the tinsel fairy there.

I tried putting them on a a hot plate. Let’s just say that I’m glad the ingots were inside a pie tin.

[jsanch03]

I’ll add my 2 cents since I run the 130gr 9mm mold with 8 cavities. I’ve found that adjusting your sprout pour is a must do since the sprue holes are so close together. After preheating the mold during the start of a casting session the flow of the lead I had set began pouring into the next hole before I was even done with the first hole.

[AndyC]

No extra info to add, you boys covered everything and more that I was planning to say, so I'll just confirm that love my 8-cav MP 9mm mold - best 9mm mold I ever owned.

[kevin c]

jsanch03:

That’s a good point about the spacing of the sprue plate holes. Spillover happens really quick, which for me makes controlled pours more difficult.

It helps to reduce the flow rate from the spout, be aware of the direction of the flow coming out (it is NOT always straight down), align the mold and pull or push the mold in a straight line under the flow, and angle the mold over the guide slightly away from the direction it’s being moved (at a good pace).

A nicely controlled pour can have a very symmetric sprue, not only from side to side but also in the pattern of hardened ripples over each hole in the plate.