Question about the right mold and alloy temp

[bmac1949]

I'm using a B&G #130 mold that casts 185 gr .45 boolits. I preheat the mold with a butane torch and set it on the furnace set at about 750 degrees. once the mold is hot I cast 3 or 4 times to make sure the temp is right. Everything seems ok except that the boolits are coming out frosted at the base and progressively shinny at the meplat. If I turn the furnace up the whole boolit has a dull finish. The boolits are fine other that this and it probably doesn't amount to much but I was wondering if anyone can tell me what is going on? Thanks for your response.

[geargnasher]

You don't say what alloy, but if it contains any tin at all, keep your furnace temp well below 750, like 725 max, or you defeat the entire purpose of tin.

If you're getting frosty boolits at all, we can assume you have an alloy that contains a few percent antimony. Frosting is entirely a product of MOULD temperature, not the temperature of the alloy you pour in it. If your bases are frosty and the noses shiny, one could say that the bottom of the mould is too cold, or the base is too hot, depending on your preference for all shiny or all slightly frosty boolits. Either way you have uneven heat in the mould. Keep casting at a steady pace and it will even out, or use an open-coil hotplate to heat the mould from the bottom and cast at a steady, brisk rhythm to keep the heat going in the mould. Excess frost, the king that leaves pits and makes the boolit surface look like broken cast iron or like it was sandblasted, is from a mould that's WAY too hot. I like a light, satin frost that will wipe off with a twist of a dry rag when the boolits cool, leaving a bright satin surface beneath. I find it's easier to get good fillout this way, others prefer to run a cooler mould that drops shiny boolits, but it's really easy to get rounded edges and bases and general poor fillout that way, with me doing it. Your results may vary.

Essentially, use a supplemental heat source like a hot plate to get the mould preheated to casting temperature, and control the temperature of the blocks with your casting speed. Control your sprue plate temperature by the size of the sprue puddle you make on top of it.

There are numerous other tricks to keep mould temp even on certain moulds if necessary, like using a damp sponge to briefly "quench" the sprue plate if it gets too hot and even minimum sprue size still overheats it. You can use a small fan to cool the sprue plate, and you can hold the mould upside down for a few seconds after you cut the sprue but before opening the blocks, this will encourage heat to rise through the blocks and go toward the nose of the boolits.

But 98% of the time, just a brisk, even pour pace of 3-4 pours a minute (TIME IT!) with alloy that's 100 degrees hotter than it's full-liquidus state does just fine. Don't pause with the mould blocks hanging open while you inspect the boolits you just cast, in fact don't worry about how they look for the first few pours, just concentrate on a steady pace for a while and focus on keeping a smooth cadence of lead going through the mould. The heat will even out and take care of itself in 10-20 pours in most cases. If the boolits get too badly frosted but it's even all over, just slow down your pace a bit, the mould will cool off very quickly on its own.

Gear

[ShooterAZ]

Maybe preheat the mold with a hot plate, rather than the butane torch would be my $.02.
I am guessing you are applying the torch (very hot) to the bottom of the mold?...hence the frosty at the bases.

[bmac1949]

Thanks for the response. You've given me a great deal to work with. I can see that, first off I need to slow it down some. BTW I'm casting these out of WW

[bmac1949]

Actually this is happening well after I've preheated the mold and out of about 300 boolits that I cast today most were like I described except for when I turned the furnace up. This caused them to come out of the mold frosted and pitted. I threw those back in the pot. But your're right that I haven't got the mold evenly heated yet. Thanks

[462]

My mould pre-heater.

[odfairfaxsub]

i put my mold ontop of the pot that the lead is melting in and i put aluminum foil over the mold/pot set up

[runfiverun]

a mold thats about 400*f will allow you to use a cooler alloy in the 675-700 range.
if you are able to keep a consistant pace thats faster then gears recommended pace then you can turn down the alloy temp.
i used to be able to cast at 615* alloy temp with a 2% tin ww alloy. [that's lower than the melt temp of pure lead]
the bullets have to fall out of the mold as soon as you open it to keep a mold hot at this pace/temp.
i'm in the 675 range now. [gettin old sucks] and usually start at 725 and go down as i move along and hit a rythmn.
usually to 715, then to 700, then to 675.
if i stop for any reason [usually to sit down because my back starts to hurt] i turn the temp back up to the next setting and set the mold back down to be kept warm.

[bmac1949]

Thanks again for the advice. I'll start trying these techniques this evening when I get time in the shop. I'll see what works for me.