Alloy Hardening Question

[blue45colt]

I have a question about alloy hardening after casting.

I have several boxes of swaged .357 cal. bullets that test out at 9 BHN on my LBT tester. These are very consisted box to box.....all right at 9.

I have old Lyman 454424 HP mould that I wanted to cast some soft HP's, so I melted some of the swaged bullets, thinking the 9 BHN would be about what I was looking for the get some expansion at around 800/900 fps. I added no tin and allowed to air cool. The pot was empty and clean before the melt.
The resulting bullets are testing 11/12 BHN.

Anyone have any idea what is causing the increase in hardness?

[KYCaster]

Welcome to the forum.

Unlike steel, working lead alloys softens, rather than hardens, so a swaged bullet will be as soft as the alloy will permit.

Pure lead is 5 BNH, so at 9 BNH your bullets contain some alloying metals, probably .5% Antimony and a trace of Tin and Arsenic. When cast in a mold and air cooled the speed of cooling will have some hardening effect.

They can be annealed by heating in an oven to ~350 deg. and then turn off the heat and allow them to cool in the oven. The slow cool should soften them to the same 9 BHN as the original swaged bullets.

Jerry

[Buckshot]

..............blue45colt, welcome to the board. Those swaged boolits you have may have started out their life at the hardness you're seeing now. If you're wanting soft for hunting, those newly cast ones should be fine at handgun ranges and hunting velocities. If that was the issue.

..............Buckshot

[mbk]

Let me see if I can ask this where it makes sense. I inhereted a bunch of casting odds and ends from a cousin who cast bullets a lot for many many years. When I cleaned out his shop I came up with about a couple 5 gallon bucket of odds and ends bullets that had been setting out in various containers over the years since he quit casting and had got wet and dirty. He had a good supply of Linotype, tin, lead, etc. and always cast up fairly hard bullets. I don't think he ever had a hardness tester but alloyed by proportions and weights of know materials. I was going to melt down the neglected bullets to start my casting with. I had assumed (appears incorrectly) they should come out about the same hardness as what he had cast origianlly. Will they be harder than what he had cast up or softer. Being unkown alloy, to anyone still among us, would I be better off buying a hardness tester of some sort and just starting over rather than guessing? I know just enough about casting from watching him years ago to be semi dangerous.

Thanks, Mike

[imashooter2]

Let me see if I can ask this where it makes sense. I inhereted a bunch of casting odds and ends from a cousin who cast bullets a lot for many many years. When I cleaned out his shop I came up with about a couple 5 gallon bucket of odds and ends bullets that had been setting out in various containers over the years since he quit casting and had got wet and dirty. He had a good supply of Linotype, tin, lead, etc. and always cast up fairly hard bullets. I don't think he ever had a hardness tester but alloyed by proportions and weights of know materials. I was going to melt down the neglected bullets to start my casting with. I had assumed (appears incorrectly) they should come out about the same hardness as what he had cast origianlly. Will they be harder than what he had cast up or softer. Being unkown alloy, to anyone still among us, would I be better off buying a hardness tester of some sort and just starting over rather than guessing? I know just enough about casting from watching him years ago to be semi dangerous.

Thanks, Mike

Just one man's opinion...

They were bullets once, melt them, cast them and they'll be bullets again. This hobby can be as simple or as complex as you choose to make it. There's plenty of time to get into the minutia in the future.

[MakeMineA10mm]

I agree with Imashooter pretty much.

If your cousin cast "fairly hard" boolits, you may also consider going 50/50 of his old bullets and WheelWeight metal. It's hard telling what he used, but if he made them hard via formulas, there's probably a lot of linotype and tin mixed in his bullets.

We (boolit casters in general) have re-learned what the old-timers knew - that at moderate velocities (<1300fps) not only do we not NEED a hard bullet, it is often a detriment... I'd use dead-soft lead (cable-sheathing, etc.) or Wheel Weights (the cheapest, most common relatively-soft material available) and mix those bullets with that softer material 50/50. You'll probably still wind up with medium-hard bullets (harder than generally needed) but you'll stretch out much farther the expensive tin and antimony that your cousin collected (and you'd have to pay to replace at the high prices of today).

[Buckshot]

.............A lead hardness tester is nice but not a necessity. To a degree it will allow you to duplicate successfull alloys you've used before, and it will allow you to 'assay' any unknown scrap you glom onto. You may also run tests of varying hardnesses for loads you are working up.

WW used to be in the 11 to 12 bhn area, but these days seem to be a couple points softer on average. I doubt this really is a big deal for general shooting. As your loads intensify and do well, it's nice to be able to blend up a batch of the same hardness.

Tin will harden lead to a point but it's expensive. Antimoney does a much better job, and goes well beyond what a lead-tin alloy can be hardened to. But an antimony-lead alloy is a pain
to cast, can be brittle and will lead. Tin has to be added to it. An antimony-lead and a tin-lead alloy can both show the same hardness, but only the tin-lead alloy will be useable. The hardness tester won't tell the composition. Just the hardness.

...............Buckshot

[blue45colt]

KYcaster, thanks for the input on the swaged alloy.
I'll try the oven annealing on some and see what I end up with.

Buckshot, you are correct. These should be fine for standard revolver velocities.
I just wanted to get the most expansion possible at the 800/900 fps range.
This mould has fairly thick walls and I think a softer alloy would be of some benifit.

Thanks again

[grumpy one]

mbk, how hard the bullets are depends both on the alloy, and how it's dealt with - if it contains antimony. The hardness of lead-tin-antimony alloys depends on their cooling rate. As an example, if I cast my 1.3% tin, 5% antimony, 93.7% lead alloy in a very hot mould so all the bullets come out frosty, and I slowly air-cool them, the bullets average 13.6 BHN. However if the mould is not so hot - barely hot enough to get perfectly-formed bullets, so they come out shiny - they average 24.5 BHN, which is harder than air-cooled linotype. In other words, the hardness of alloys containing substantial amounts of antimony - especially in the region of five or six percent - is greatly affected by cooling rate. Just by pouring that alloy into a Lee aluminium ingot mould that is already moderately hot, the ingots vary from 16.6 BHN to 22.7 BHN, and average 19.5 BHN. Even an aluminium ingot mould making one pound castings can chill them fast enough to harden an alloy containing a fair amount of antimony.

If you use an alloy with say 4 to 7% antimony, you should either be very, very consistent in the way you do your casting, or you should heat-treat the bullets after casting. If I had annealed my shiny bullets they'd have dropped back to 13.6 BHN. I found it easier to toss them in the scrap instead, because I find heat-treatment a PITA, but for a new caster it is well worth considering - it is unlikely that your first few batches of castings will have uniform mould temperature, melt temperature, and cooling technique, so you could find yourself with a very wide range of hardnesses, which is likely to be unhelpful to accuracy. Of course if you like heat treating bullets, it is a very useful technique - you can use a cheaper, lower antimony alloy and choose the exact hardness you want, anywhere between say 10 and 30 BHN, long after you've cast them. You can also cast them soft, size them very easily, and still shoot them at anything up to 30 BHN if you need them that hard. All you need is a thermometer, a toaster oven, and a bucket of water.

[Bret4207]

We it me, I'd melt the whole bunch. Thats' minus any boolits I think I might like to shoot. You can wash them off in hot water and relube. But melt the remainders and cast a few to see how much deformation you get. Soften with WW or lead if too hard. You might just have what we refer to as "enrichment alloy", ie- an alloy with a lot of the expensive stuff like tin and antinomony in it. If so use it sparingly as it's a pain to replace.

[Ricochet]

As for cable sheathing, I'd often read that it's "pure lead," and it is rather soft stuff. But The Metals Handbook says that the typical cable sheathing alloy has something like .028% calcium in it, which age hardens over several months even if extruded cold, and it creeps and sags in use a lot less than unalloyed lead. Calcium, while not generally recommended for casting, is one of the alloying elements that the Key to Metals article on heat treating lead alloys says will harden by precipitating with aging from a solid solution. The very soft scrap I've found to harden up about like ACWW after quenching and aging has a good bit of cable sheathing lead in it.