Heat treating cast bullets
I have been experimenting around with my 45-75 Chaparral 1876 for over 2 years now, and have a question regarding heat treating cast bullets for it. I found that by dropping the wheelweight alloy bullets out of the mold directly into a bucket of cool water that the bullet is substantially harder and that it shoots way better. Now i heard that the heat treatment slowly leaves the alloy (ie: the crystals slowly grow bigger and thus the alloy gets softer) over time. My question is, what is the time frame? Also heard the softening can be slowed by freezing the bullets. I am conducting the experiments myself right now (some sitting out, some in the deep freeze. Will test them in a hardness tester every 3 months or so). I just dont want to reinvent the wheel. Has anybody already tested this?
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I am not a metallurgist but have never heard of crystals "growing" in metal without some induced chemical or mechanical action being performed on the metal.
I do "quench" cast bullets by dropping into a bucket of water straight out of the mold, this hardens the surface of the bullet slightly although I have never put a hardness tester on one to actually measure any difference. Never heard nor can I imagine how this could change over time.
As far as putting bullets in a freezer to make them harder, I never heard of that either nor can I imagine what process could be taking place in temperature ranges a normal freezer experiences.
Extreme temperatures can induce changes in metal but I don't think a refrigerator is gonna do it.
Dan R0 -
I have heard the same thing, that the bullets will soften to their prequenched state over a period of time. I kdon't know the answer but thirty years ago when I was casting I did the same by dropping them into a 5 gallon bucket partially filled with cold water. For handgun velocities I found no leading issues in the barrel and I still haver reloads that 25 years later still appear to be hard. At the time for handgun bullets I was using 1/2 wheel weights and 1/2 soft lead. 0 -
quote:Originally posted by SP45
I have heard the same thing, that the bullets will soften to their prequenched state over a period of time. I kdon't know the answer but thirty years ago when I was casting I did the same by dropping them into a 5 gallon bucket partially filled with cold water. For handgun velocities I found no leading issues in the barrel and I still haver reloads that 25 years later still appear to be hard. At the time for handgun bullets I was using 1/2 wheel weights and 1/2 soft lead.
An interesting read:
http://www.lasc.us/HeatTreat.htm
I was suprised at how well lead alloys responded to heat treatment.0 -
the lyman cast bullet handbook has all the info on heat treating cast bullets. and also says they will soften with age. 0 -
What's the advantage of heat treating instead of adding a little more antimony to the alloy? 0 -
Thanks guys! Don, I am printing that out and will read it at work today.
Dan, as far as crystals growing, this definitely happens...I guess the molecules align themselves into patterns with time or something like that. Freezing them slows down this migration. I did not intend to imply that freezing does the actual hardening...it is the quench that does the hardening. Freezing hopefully keeps it that way. My background is in geology, and I know a melt that solidified fast has rocks and minerals with fine grained crystals, while a slowly cooling magma gives large crystals (uh oh...how did I get geology in a gun forum...).
With steels it is different. The heat treat there actually changes the structure of the crystals, as well as the size. To get technical, face centered versus body centered crystals. But with lead alloys I believe it is not structure but size of the crystals.
Glabray, the reason is because I hove lots and lots of wheelweights at my disposal...I do have a limited amount of other bullet alloy I use for my hunting and target loads, but for plinking and general shooting I want to develop a load that uses my wheelweights.0 -
quote:Originally posted by glabray
What's the advantage of heat treating instead of adding a little more antimony to the alloy?
I think the article linked to above states that there is ADDED advantage to quenching ABOVE just adding antimony.0 -
Most metals exist in a crystal matrix system. There are three primary variants of these:
Body centered cubic
Face centered cubic
simple cubic
There are several different subsets and variations, but for metals those are the prime ones.
The lattice solidifies differently for different metals. These are known as solidification phases.
http://ase.tufts.edu/mechanical/thermal/steel/Image2.gif
The diagram in the link is a modified weld research council 92.
When you have any alloy (lead, tin, antimony for instances) the constituent metals solidify at a specific temperature.
Lead is a face centered cubic
tin has an odd ball crystal form called tetragonal diamond cubic
antimony has yet a different crystal form called rhombohedral
Their constituent forms melt together in specific percentages to form an alloy that is relatively tough.
Being more specific, dropping a freshly cast bullet into a bucket of water does in fact drop the alloy through the lower transformation and temperature range rapidly.
http://www.metal-mart.com/Dictionary/dictlett.aspx#I29
(Temperature range over which a chemical or metallurgical change takes place.)
This 'quenching' alters both the chemical and crystal lattice formation.
Ideally, the bullet should be held onto and only quenched a short time and allowed to air cool.
By doing this, the outside of the lead bullet basically does become harder, but it also creates a stress stratification zone between the bullet core, and the bullet exterior.
Whether or not the bullet over times becomes soft again depends on the nature of the allow cooling etc. Normally they will retain it, but the wrong alloy has been known to soften over time as that stress will be working to relieve itself. This can cause dimensional problems in the long run as well.
There are a lot of methods to alter the characteristics of metals, and it would take years to get them all (Been doing it for 25 years and still don't have it all and never will).
This should however, give a little bit better idea of what is going on.
quote:Originally posted by dandak1
I have been experimenting around with my 45-75 Chaparral 1876 for over 2 years now, and have a question regarding heat treating cast bullets for it. I found that by dropping the wheelweight alloy bullets out of the mold directly into a bucket of cool water that the bullet is substantially harder and that it shoots way better. Now i heard that the heat treatment slowly leaves the alloy (ie: the crystals slowly grow bigger and thus the alloy gets softer) over time. My question is, what is the time frame? Also heard the softening can be slowed by freezing the bullets. I am conducting the experiments myself right now (some sitting out, some in the deep freeze. Will test them in a hardness tester every 3 months or so). I just dont want to reinvent the wheel. Has anybody already tested this?0 -
bullet alloy is no different than other metal alloys. Quenching does alter the crystal formation, crystal lattice, and to some degree, chemical formations.
quote:Originally posted by dandak1
Thanks guys! Don, I am printing that out and will read it at work today.
Dan, as far as crystals growing, this definitely happens...I guess the molecules align themselves into patterns with time or something like that. Freezing them slows down this migration. I did not intend to imply that freezing does the actual hardening...it is the quench that does the hardening. Freezing hopefully keeps it that way. My background is in geology, and I know a melt that solidified fast has rocks and minerals with fine grained crystals, while a slowly cooling magma gives large crystals (uh oh...how did I get geology in a gun forum...).
With steels it is different. The heat treat there actually changes the structure of the crystals, as well as the size. To get technical, face centered versus body centered crystals. But with lead alloys I believe it is not structure but size of the crystals.
Glabray, the reason is because I hove lots and lots of wheelweights at my disposal...I do have a limited amount of other bullet alloy I use for my hunting and target loads, but for plinking and general shooting I want to develop a load that uses my wheelweights.0 -
What you have created is a paralax matrix that can not be identified or solidified by the hardness of the rockwell with out he third lunar eclipse aligning with the fourth Sunday in March. Then and only then will you have achieved the knowledge you seek to obtain your answer.
Signed
Grasshopper0 -
QUESTION????? If you quench a cast bullet(s) right out of the mold... and this hardens the surface...What happens to that hardened surface when you run them thru the sizer????
Thanks,
JIM..............0 -
Don, your link has an answer in it...the fellow at LASC tested 10 year old heat treated bullets and found they had only softened a little. That was what I needed to know. I can go ahead and load up 200 or so rounds and if it takes me a year or so to go thru them they will still be as hard as when I cast them. I also learned NOT to skim off the antimony from the top of the melt (I had been doing that but didnt know it was antimony[:I]). That article was excellent. Thanks again.
Jim Stark, read the lasc article, he answers your question, basically running them thru a sizer can work soften them. I dont size my bullets so I didnt pay much attention here, but believe he says to size them before he oven treats them. If you water quench like I do, well, sizing may work soften the surface which is probably not what you want.
Plan on (finally) having some time to myself this weekend, where I will read the other links that readers have been kind enough to post. Thanks guys.0
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