Assembly, cleaning, prepping, lubing
I start by cleaning the mould with brake cleaner, including the pins and the screws that hold the pins in. You can clean your new mould with warm water first but I don’t. Miha is generally doing a god job of removing any oils and debris from the moulds. I then assemble the mould, placing the HP pins I want to use in it, then backing the HP pin screws off about a 1/8 turn to prevent the pins binding in the mould.
Preparing a new brass mould: Heat cycle it on a hot plate. I put a bit over half power on my switch, not too high, and not too low, bringing mould to approx. casting temperature. I then switch off the hot plate and let the mould cool by itself. There is no need to take the mould apart when heat cycling. Keep everything together and make sure you have the pins inserted as well. Cycle three or four times, let it cool every time, when you're done, everything will be set in. This starts the patina building. Just casting with it keeps the process going on too. Patina prevents sticking and bullets generally drop out.
Lube the screws that hold the HP pins in place. I lube the pins that hold the moulds inside handles. You can take a graphite pencil to coat the HP pins, but coat only the part that will make the HP. Repeat that after 4 or 5 sessions. Place a single drop of sprue plate lube (you got it with the MP mould) on the shafts at the outside of the blocks. Just a drop of oil will lube the shafts without contaminating the cavities.
Casting with HP brass mould
Preheating . Carefully heat the mould on a hot plate to bring it up to casting temp or until the sprue plate lube starts to smoke a bit. MY hot plate is set slightly over medium. I now always use a hot plate to pre-heat my moulds. That way I don’t waste time filling them too many times just to get the mould temp. where I want it. With HP pins, I sometimes still need to do many pours, but properly pre-heated mould and 3-5 fills is all I need. This way, with non HP version, even the first pour can be perfect. But the longer the pins (and larger the HP), the longer I leave it on a hot plate. Pins have to reach the proper temperature too. So they sit on hot plate for 20-30 minutes mostly. In that time my casting furnace gets ready.
Tin. Use some tin in your alloy when casting hollow points. Tin helps boolets to expand (that’s why you cast HP, don’t you?) and also casts well with a hollow point mould. I mostly use WW's + pure lead (50/50) with 2% tin to the final mixture. If you powder coat you can be less careful with your alloy and you can simply use pure lead with 2% tin.
Temperature. Since I use a bottom pour electric furnace with PID I can control alloy temperature. I use 750F/400C for rifle HP and 680F/360C for non HP pistol mould. This is not a rule, more of a guidance. Remember, if the temperature of the pins drops, things can happen. So, especialy at the beginning, fill the cavities front to back generously and even to keep the heat in the cavities. Hot pin is a trouble free pin. You can also raise alloy temp. up and adjust the speed of casting to balance any overheating. When you find that happy medium between too cool & too hot, casting becomes pleasure. If you bottom pour, be sure that you don't pour directly in center, but rather slightly off. Longer the pin, more important is that. That way alloy will not hit the pins first and will not cool down. So, do not pour straight on the pins, try to hit the hole of center and »miss« the pins.
After the lead is poured, wait and watch the lead change colour as it solidifies, watch for the little sink mark to show. After the sink mark, wait couple of seconds and tap the sprue plate with a wooden stick. My stick is covered with layers of leather for less stress. Sprue plate must cut the sprue off – bases should not tear and smear lead. Cutting should leave a clean flat base of the bullet. If you see smearing of bases – it was to soon. If the sprue cuts a bit to hard, you waited to long. If the bases are not filled out, use more pressure when pouring.
You can do that by bringing the mould holes closer to the spout, or open the pressure on that spout. But usually, just pour enough lead so that even after the sink mark, you still have one big continuous sprue. Remember, big sprue keeps mould and pins hot. If you think you can't find a rhythm, then: fill the mould, count to 3, open the sprue plate, count to 3, open mould and dump. Repeat.
So with rifle HP moulds (when casting really hot!) after the sprues are cut off, wait another couple of seconds, then turn the mould upside down. Tap on the bolt on the handles to help with mould opening. Tap first and let the tapping open the mould, then help with handles.
This will usually help open the mould and will at the same time push the side pins out.
MP MOLD Crammer style pins pulls the bullets out of the cavities when the mould is opened. You can help pins to be pushed with your wooden stick too, but usually they just drop out. After the mould is opened and when temperature is correct, the bullets will fall off the pins. If they don’t (mostly if I have a blank FP pin inserted), gently tap on the mould handle bolt a couple of times until they do. If the bullets take more than a couple of taps to fall off the pins, the moulds and the pins are too cold.
Observe sprue and bases . It not so much about alloy temp., it is about casting tempo that actually controls mould/pin temp., more than alloy temp. Watching the sprue and how long it takes to harden tells much about mould temp. Speeding up or slowing down - casting cadence - let you stay in the perfect zone. So after preheating brass HP moulds and after a few pours, the sprue puddle will remain liquid for a couple of seconds. But when the sprue puddle takes three or more seconds to harden, you are ready to start. This means if you count two seconds then tilt the mould, the still liquid sprue will pour off like water. After three, it will not. This will work at any melt temperature. Below 550F/290C you will (might) have trouble with the furnace nozzle (spout) freezing. Above 750F/400C your surface will oxidize quickly. When the sprue takes 4 seconds to harden, slow down, cool your mold or drop the temperature of the alloy - if you can control it.
When you get the temperature and rhythm, and everything seems right, keep your casting cadence and inspect your boolets closely only AFTER you finish casting. Admiring them for to long can ruin your “perfect zone”. Rather stay focused on the solidifying of the sprue and watch the bases for when you should cut the sprue. If your bases smear – you cut the sprue too soon (mould is too hot). And don’t think to much. Each mould has its own “personality”, or as I say “preferences” and it will tell you how to handle it. Write down (or remember) for each mould at what alloy temperature you cast, what was the setting on a hot plate and for how long it was there.
Casting with hot alloy in the same direction, with 6cav or even 4cav, can cause hot and cold sections in the mould. Solution - alternate your casting front to back cavity and back to front . Usually the cavity which was filled the last is hotter than rest. It can smear. Observe bases. Alternate. Slow down if necessary. Use wet cloth to cool that hot part of the mould. Remember - your casting tempo controls temperature. But also casting front to back and back to front helps spreading the temperature of your mold equally.
Lubing the sprue . During casting I occasionaly lube the sprue plate. In approx. 1 hour of casting I do it 4 – 5 times. There is no rule. And lubing during casting is not really necessary but it lubricates the sprue plate, reduces wear and instantly removes small lead particles. I use small cotton rag, slightly oiled with 2-stroke mineral chain saw oil. I pour lead into the mould, cut the sprue, then I lightly wipe bottom side of sprue and top of the mould - with boolets still in cavities. I noticed that this helps releasing boolets and it doesn't affect my ability to powder coat them later at all.
End of casting. When I quit casting I wipe the sprue plate (still hot) top and bottom for the last time. This prevents the sprue plate from rusting and removes small lead particles. No need to lube cavities and inside the mould – brass will not rust. And when that mould (with lightly oiled sprue plate) is put on the hot plate next time, oil will start to smoke; again an indicator that mould is ready. Before casting and before pre-heating, you can also remove that oil with brake cleaner and toothbrush and then lightly oil/wipe the sprue plate bottom and pins with oiled rag or q-tip.