Heat Treating Question

[Jim Flinchbaugh]

Well., not so much on the treat part, there a gazillion posts available using the search function.
What I haven't been able to find is:
Do oven heat treated boolits retain their hardness over a long period of time?
In other words, if I cast, and heat treat a coffee can full of boolits, will they stay hard if they sit around for 2-3 years?

I thought I read something about this once, but I couldn't find it.

[huntrick64]

Jim, I have poured over the mass of info regarding this subject over the last three years. I got "stuck", if you will, going down that road while casting for a 40 S&W. Was somehow convinced that I had to have BHN 25 bullets for that caliber, but that is another story. I found the most usefull and accurate info to be in the following article from the LASC site, http://www.lasc.us/HeatTreat.htm. This guy tested some bullets that were heat treated to BHN=30 over 10 years ago and they were still BHN=26! That's slow enough for me to no worry about it.

Two biggest things I have learned over that time:
1. I didn't really need a high BHN when fit and lube were correct.
2. If you do treat them, size them immediately after quenching before their BHN begins to rise, or it will tear up "any" sizer over time. By immediately, I mean within an hour or two. Wait more than that and you will see what I mean.

If you haven't checked out the LASC site, do so. Wealth of info there and Fryxell's articles are tops!

[cbrick]

huntrick64, thanks for the compliments on the article and the web site.

I size & seat checks after casting and before heat treating. Once heat treated I run them through the lubrisizer with a die .001" larger than than they were sized with to lube them.

When heat treating too much of a good thing ain't really a good thing. It is a rare bullet that needs to be upwards of 20 BHN. Water quenching will get you into a max needed hardness range but convection oven heat treating results in a much more consistent outcome assuming all bullets in the HT batch are from the same batch of alloy.

Rick
lasc.us

[Dusty Bannister]

I have seen the bases of the castings, just above the gas check start to melt due to the heat transfer from the gas checks. For that reason, I heat treat and quench, and dry the bullets. Then attach gas checks, lube and size and do not delay. Avoids the risk of water getting between the check and the base of the bullet. Two hours means the hardness process has already started and if for no other reason than less effort, should be avoided. Dusty

[cbrick]

I have seen the bases of the castings, just above the gas check start to melt due to the heat transfer from the gas checks. Dusty

At what temp are you heat treating and how hard are you trying to acheive? If your getting any signs of any melting at all your oven is set too high gas checks or not.

Rick

[Jim Flinchbaugh]

As for sizing post heat treating, not gonna happen here.
If you smear the surface of the lead by sizing after heat treating,
you've just wrecked your process IMO.
I was wandering about the gas checks causing an issue during heat treatment though.
Oven treating is what I'm gonna try.

I'm not going to go nuts treating bullets till I know it works for what I want, but if I get there,
It's nice to know I can make a bunch and have them ready to go.
Thanks fellers!

[cbrick]

I was wandering about the gas checks causing an issue during heat treatment though.


While I size & gas check prior to HT whether or not the copper check absorbs heat fast than lead or not has little to do with it. If the oven's temp is set high enough to melt lead checked or not it is going to melt lead. If the oven temp is set below the melt temp of the alloy it wouldn't matter if the check gets to that temp before the alloy, it will not get hotter than the oven temp and won't show signs of melting. If you are seeing anything such as what looks like blisters starting to form on the bands your oven is too hot.

If you quench the WW bullets that are this hot you will age harden to around 30 BHN, much too hard for most all applications.

Rick

[sqlbullet]

I size after heat treating and the bullets still test plenty hard. Sizing doesn't work the lead deep enough to matter. The lands will cut 3-4 times as deep as sizing will. YMMV.

I ran some tests on a series of samples a few years ago a couple days after casting and then a year after casting. The bullets were isotope lead, there were 18 groups of samples and each group had a different casting temp/heat treatment. Some were air cooled, some quenched from the mold, some oven treated without quench and some oven treated with quench.

They were broadly categorized as 'soft' with a BHN of 9-12 and hard with a BHN of 17-30.

The soft were either part of a group that was air cooled, or had as a finishing treatment that included heating in oven and cooling in place which removed any heat treatment. After a year these had all migrated to 12-15. In all cases these bullets were harder than the measurement a few days after casting.

The hard bullets all ended their cycle in water, either direct from the mold or from the oven. After a year these were all between 21 and 24 bhn. There were examples of bullets getting both harder and softer over the year. The bullets were all moving toward a BHN of 23 it appeared.

My interpretation of these results is that there is an optimum matrix/BHN that a given alloy will reach. While you can force the hardness above this in the short term, over time your allow will cure towards this optimum level. For my isotope alloy this number appears to be BHN 23.

[Dusty Bannister]

At what temp are you heat treating and how hard are you trying to acheive? If your getting any signs of any melting at all your oven is set too high gas checks or not.

Rick[/QUOTE]

I am using a toaster oven, with a layer of foil on top of the basket of cast bullets. Temp set just below melting of plain cast bullets as most oven thermometers are a close guess. I have never had an issue with plain based bullets. I use a power strip for the on/off power supply. Anticipated use of these were specifically for the AR-15. Lots of other options, but I wanted a consistant batch of bullets to work with, and wanted hard bullets that fit the throat. This was to be made from my normal casting alloy used in handguns. Being "too hard" was not a consideration. Many use linotype for this purpose as well. I was looking at relatively inexpensive practice ammo for Junior Shooters without the expense of jacketed bullets.

[popper]

I agree with sqlbullet. Sizing may decrease the surface hardness, but the core will still be hard. Think about what happens when the rifling work softens the alloy.