Casting Pure Lead at High Temperatures?

[rsterne]

I haven't done a lot of boolit casting, and my interest is in casting pure lead (I actually use 1% tin) for airguns (.257 cal and up).... I only recently got a thermometer, and I'm still getting used to using it and trying to determine the optimum temperatures.... Today I was casting .358 cal Lee aluminum molds, the 125 gr. FN and the 150 gr. RN.... I cast the heavier ones first, at between 700-750 degrees, and even after the mold was warmed up, I was getting a bit of wrinkling.... The bullets were well filled at the base, with only about 10% discards.... but when I was sorting them I noticed that most had a few small wrinkles.... Too cold, right?....

When I cast the 125 gr., I raised the temperature gradually, and as I did, the bullets just kept getting better and better.... I wondered how far I could go before seeing any frosting, and even at 950 only some small areas near the base showed any dulling.... I backed the temperature down to 850, and cast most of the bullets at that temperature.... When I sorted them, I had a few of the early bullets that looked like the 150 gr. with a few small wrinkles.... The ones that had a dullish area near the base seemed to also, in general, have a slight flash on the edge where it looked like the sprue cutter had shaved the edge slightly.... as least I think that was primarily on the ones cast at over 900.... Basically, however, the 125 gr. (mostly cast at 850) were far superior in appearance to the 150 gr. which were cast at 750....

My question is this.... I see in the recent survey that the largest number of people case between 700-725.... Is that for alloys with a significantly lower melting point than the nearly pure lead I am using?.... Is there any reason I shouldn't cast at 850?....

Bob

[Bullshop]

I have a custom casting service and so cast a good number of pure lead conical boolits for ML shooters. I get no complaints about quality because there is nothing to complain about. My method for casting pure lead is simple, the dial gets set at the full on position as high as it will go.
A bit more oxidation at the surface of the pot, maybe but the quality of the castings is worth it. You can cast good sharp clean lines with pure lead but it has to be HOT!

[btroj]

When I cast pure lead I do as Bullshop does, pot goes on full tilt. Always works well for me.

[rsterne]

Thanks for the responses.... So is the "frosting" (which is supposed to indicate too hot) a function of alloying metals (Antimony or Tin?) that you don't get with pure lead?.... or will it occur at some temperature, and if so, what is that?.... What about 40:1 (2.5% Tin).... is there a maximum temperature for that, and if so, what?....

Bob

[Bullshop]

""So is the "frosting" (which is supposed to indicate too hot) a function of alloying metals ""
Yes, from antimony
Pure lead will cast blue if your mold gets too hot. Drop the melt temp a little at a time until the blue stops if it bothers you.
I like for them to show a little blue hue so I am sure things are hot enough for good fill.

[melloairman]

Hello Bob .Just to keep things straight . BB air rifles start at 30 caliber and go up . What you have are small bore air rifles . You have good talent and do good work . But they are what they are and we have had this discussion on other forums . Please talk to DAQ , Randy Mitchell , or Dan McVeigh . They will all tell you what I have stated . They all have made 25 caliber to 72 caliber air rifles . And are known as BB makers . But they state BB start at 30 caliber . Marvin

[freebullet]

In my limited experience melting nearly pure lead, I've found it builds up an oxide crust that must be refluxed often. Is that normal? I figured it is because of the higher temp.

[btroj]

It does build up an oxide film. I find that if left alone it tends to be self limiting.

[runfiverun]

the mold temp will also dictate fill out.
I don't run my soft lead at full tilt but I do have the mold hot enough to feel the heat coming off it from 6" away.
I also keep a layer of ash or kitty litter on top of the alloy.

[rsterne]

Marvin, I removed the offending words "big bore" from this thread.... hope you're happy with that.... I assume you noticed I was talking about .357 here?....

Bob

[rsterne]

Bullshop.... I thought perhaps it was the Antimony that caused the "frosting", thanks for the confirmation.... Nice to know that unless I'm getting a blue colour I'm not too hot, and even then it's only a cosmetic thing.... MUCH APPRECIATED....

Bob

[44man]

I set my Lee pot at 8. I cast tons of pure for ML's, etc. Just need a little more heat because pure does not flow as well as with added tin.
I ladle cast and make perfect boolits with a 30 to 1 lead tin mix, from 500 to 560 gr for BPCR. Pure casts just fine too. It does NOT need over 800*, just control mold temps. Actually, I cast the very same way as I do with any alloy, just a little hotter for the pure lead.

[cbrick]

Any reason you shouldn't cast pure lead at 850 degrees?

No but . . . Your not casting pure, according to post #1 your casting with 1% Sn added. The metallurgy of Pb/Sn alloy dictates the tin cannot do what you put it in the melt to do past about 750 degrees. Sn also oxidizes very rapidly past 750. I would suggest that if your going to cast that hot to save the tin for other purposes, it isn't working anyway.

Another consideration of higher pot temps is waiting for the alloy to cool inside the mold enough to open the mold, casting really hot can slow the casting down. One of the reasons the boolits fall from the mold is that as they cool they shrink. It takes longer for the alloy (or straight lead) to cool enough from 850+ than it does from 700-750 degrees.

Rick

[rsterne]

Well I'm still getting some wrinkles at 750, so according to that I should forget the tin and just crank up the temperature to 850 or so, whatever works for the pure lead?....

Bob

[cbrick]

Well I'm still getting some wrinkles at 750, so according to that I should forget the tin and just crank up the temperature to 850 or so, whatever works for the pure lead?.... Bob

I would say your looking at mold temp, NOT pot temp. The mold should cast quite well somewhere around 400 degrees, 750 degree alloy (pot) temp can and will keep a mold at 350 degrees less than that.

Don't look at it as pouring alloy into your mold, look at it as pouring heat. The boolits you mentioned are relatively small meaning your not pouring much "heat". Pre-heat better and cast with a faster rhythm to keep the mold at temp. Casting pure lead at 850 or so won't hurt the metal but it can sure slow down the casting. Casting a Pb/Sn alloy that hot defeats the purpose of the tin.

Rick

[Changeling]

I think your thermometer really sucks!

[44man]

No need for 850*. I set on 8 but do not know the actual temperature, never measure it. I do know that tin stays because I have hundreds of stored boolits that shine like new. Pure alone will oxidize with white crud.
It really is the mold and cadence you use.
Just because I use 8, does not mean my lead is 800*, might be 750* actual. I just got used to where the alloys cast best without a thermometer, too lazy to get it out.
Pure just takes a little more heat and tin can reduce the heat needed, so does antimony with tin. It is a feel, experience is the hardest thing to convey. After a while, you can look at a boolit and adjust without any thought.

[rsterne]

Well I can't cast any faster, and that means there isn't time to heat the mold (by resting it on a hotplate, for example) between bullets unless I want to cast REALLY slow.... so how would I go about heating the mold up?.... I'll test the thermometer next time.... if it reads ~621 while the lead is melting then I'll know it's right at that temperature, anyway....

Bob

[runfiverun]

pure lead melts at 630-f
you heat the mold prior to using it and then moderate the heat through cadence.
if it's too hot slow things down a bit if it starts to get cool then speed up the cadence.
when I am doing 36 cal round balls I am using a single cavity mold so I pour open and dump then close and fill again.
just like that no counting no nothing.
the mold goes directly from the spout to open to closed and filling again.
the hand movements are in a small circle.

[44man]

Well I can't cast any faster, and that means there isn't time to heat the mold (by resting it on a hotplate, for example) between bullets unless I want to cast REALLY slow.... so how would I go about heating the mold up?.... I'll test the thermometer next time.... if it reads ~621 while the lead is melting then I'll know it's right at that temperature, anyway....

Bob

No need to do anything but cast. Forget the hotplate between pours. Don't ever get frantic. I cast at a very relaxed rate, smooth and even. I will put the mold on a piece of wood, step out to pee and continue casting. Molds do not lose heat that fast. I can use 2, 2 cavity molds at the same time and have gone to 3 at a time.
Lose the hurry stuff and relax.
Cast with me and laugh at how easy. You will look at me with crossed eyes but will never see a reject. I can cast a 20# pot, dance around the garage, tell jokes and boolits just come out.