View Full Version : Speeding production by metal duplexing

06-18-2005, 09:59 PM
I cast using 6-cavity molds for .38 spl and .45 acp, using an RCBS 20 lb. bottom pour furnace. The problem was having to frequently stop to wait for the melt to come up to temperature after adding more scrap, with a lot of down time.

I had an old 20 lb. furnace for ladle casting sitting unused. Today, I plugged both furnaces in and used the old one to melt and heat to full temperature while casting with the bottom pour. Then when the metal level got low, ladled in premelted lead and continued casting. New scrap was heating up while casting. Can't believe how much faster it is. Figuring the hours saved, having a second pot to premelt is well worth the money.

06-18-2005, 10:07 PM
actually Cheese I use a walmart hotplate (10 bucks) and a goodwill alum saucepan to premelt like you describe, I use a doller store stainless ladle to transfer molten metal to my rcbs promelt.


06-18-2005, 10:51 PM
Ought to work pretty good using two furnaces. Shouldn't be a work stoppage with that rig. You're getting to the point where you need a stoker with two pots going.

I'll bet that makes the electric meter really speed up too./beagle

07-14-2005, 07:42 PM
I replaced our electric range with a gas one in the house, so of course the electric goes into the shop. I use about a 4 quart cast iron pot. Holds oh, 90 or 100 pounds.

Using 2 six-holers I can't even begin to run out.


07-22-2005, 12:01 PM
My casting partner and I were trying this in his garage, and ran into problems getting both furnaces hot enough. Turned out that with both furnaces on the same circuit, there apparently was a drop in voltage. Even using a pretty long extension cord, moving one of them to an outlet on another circuit made all the difference.

07-24-2005, 04:35 PM
actually Cheese I use a walmart hotplate (10 bucks) and a goodwill alum saucepan to premelt like you describe, I use a doller store stainless ladle to transfer molten metal to my rcbs promelt.


Bill - I don't like alum for melting lead - I had an old alum pot that I used to smelt WW in. Club Alumn - real thick - but guess what - the molten lead was eating the alumn away on the bottem - never had an event - But I was getting real close to one when I checked it and you could see where it was eaten away.

Just my 2 cents worth -


08-06-2005, 06:16 AM
Saw a photo of a setup a guy had where he had 2 Saeco pots, one above the other, handle tied in together. When he lifted the handle the upper pot provided a fresh shot to the lower pot. Always full on the lower pot, and always hot. Of course, I can't swing even 1 Saeco pots AND I'm a ladle man. Still says alot for the guy who set it up.

08-06-2005, 09:37 AM
I use a double pot set up, a Saeco over a RCBS, along with Bruce B's speed casting method. I thought I was getting maximum production with 1 pot and two moulds till I tried the new set up. More and better Boolits than ever before!! Two shooters in the house shooting all cast for IHMSA competition. Need lots of Boolits!!!

08-06-2005, 10:27 AM
My furnace is also an RCBS 22-pounder.

As detailed in my article on speed-casting (in the "articles" at the top of the page), I use the wasted heat escaping from the top of the furnace to pre-heat my ingots.

If your ingots are long enough to span the width of the pot, place several of them across the top opening to warm up, positioned to intercept as much heat as possible. I find that a four-cavity mould for 230-grain bullets will be amply supplied, and there's no need to stop casting after adding the hottest ingot. Mine weigh about three pounds, are triangular in section and 10.5" long. and one is added to the melt as soon as the level drops far enough to accept the ingot without overflowing. I'd expect a six-cav .38 to be OK with this method, but I'm not so sure about the .45.....try it and see.

Keeping the pot full also keeps the maximum amount of heat available to melt the new ingot, as well as maintaining a constant flow pressure. RUN THE POT AS HOT AS IT WILL GO.

Using this method, but never to date with a six-banger, I never have to stop casting. I'd expect it to work all right with bullets up to maybe 200 grains in a six-cavity mould. If anyone should try it, I'd like to hear how it pans out.

08-06-2005, 10:36 AM
Bruce's method really works well. However, when cooling the mold with moisture, the cooling should actually be from the bottom of the mold rather than the top for the most accurate boolits. This has to do with how air bubbles form in the lead caused by the rapid drop of lead into the mold. There is no way to prevent air bubbles. We just have to minimize their number and size and where they are located. An air bubble, or a small stream of air bubbles, in the very center of a boolit is of no concern and will show no accuracy deviation. Perhaps at a 1000 yards the accuracy deviation might show up because of a boolit weight variation, but we weight those boolits anyway, right? ... felix

08-06-2005, 12:37 PM
The problem is Felix is that most pistol bullets in aluminum 6 cavity molds only the sprue plate needs cooling, that is at my house with my setup anyway.


08-06-2005, 12:47 PM
Bill, that's true with any mold, aluminum, brass, iron, steel, etc. It's the long boolits that will exhibit the accuracy problem, and will almost never be seen in the short ones. Now, what is long and what is short depends on all the factors you can think of. ... felix

08-06-2005, 12:56 PM

I don't seem to have any trouble with internal voids, based on the weight consistency of the bullets, but it is very important that the sprue is allowed to solidify and stop the drawing-down process that feeds the contracting alloy in the cavity. However, I do NOT wait until alll the color changes on the sprue are finished. It's clearly apparent when the sprue has taken its final form, and as soon as I see that condition, the mould is inverted and the sprue cooled on the wet pad.

When doing high-speed casting, the fast cooling of the sprue is the major time-saver in the process. Doing it by cooling the bottom of the mould will still leave us waiting for the sprue to harden, or runnning the same old probability of smearing lead on the mould top and tearing holes in the bullet bases. This would also remove most of the time saving accomplished by quick cooling of the sprue. Sometimes I do cool the bottom of the mould as well, but mostly it's a case of getting the sprue against the wet pad just as soon as it has clearly stopped changing its shape, particularly the "draw-down dimple". Once the sprue IS solidified, I don't think any air will be getting into the bullets.

When I was casting those softpoint .416s last week, and running the mould just as hot as I possibly could by floating it on the melt, it took fully thirty or more seconds to get the sprue to START setting-up by resting the mould on the wet cloth. It takes quite a while to get the heat out of the iron!

We pays our money and we makes our choices. It's all fun.

08-06-2005, 01:05 PM
Bruce, the air gets into the cavities during the lead drop into the cavity. That's probably what you intended to say, wasn't? ... felix

David R
08-06-2005, 02:50 PM
Thanks Bruce, I was doing it wrong. I filled the mold, set it on the bench, and put a wet towel over the sprue. It worked, but I see why you turn it over. Learning more every day. The pot is on, I will try it today.


08-07-2005, 11:53 AM
Bruce, the air gets into the cavities during the lead drop into the cavity. That's probably what you intended to say, wasn't? ... felix

It's not exactly what I wanted to say....

Even when I'm casting in the high-speed mode, my bullets have very little weight variation, normally on the order of less than one grain extreme spread on 200-grain bullets from a multiple-cavity mould. That indicates an absence of voids, to my thinking. On single-cavity moulds, where the potential variations are considerably reduced, the spread is much less...to the point where my RCBS 416-350s are often showing only about 1/2-grain spreads on large samples of bullets.

I fail to see how, if my bullets do NOT contain voids, they can be "helped" by cooling the mould bottom instead of the sprue. The major cause of my few rejects, and a condition I watch for when casting, is voids in the bases created by a flubbed filling of the mould.

When casting, I like to set up a swirling motion of the alloy as it goes through the hole in the sprue plate, in the belief that such a motion tends to allow air an easier escape from the alloy in the cavity. I'm satisfied that the air is exhausted from the cavities well enough for my purposes. That, in turn, allows me to cool the sprue without worrying about voids. As mentioned, we simply have to be sure that the sprue has finished supplying the bullet with molten alloy before cooling it on the wet pad.