Heat Treating Data

[pomofo]

I got interested in trying to heat treat my cast bullets after reading about heat treating at the LASC website: http://www.lasc.us/HeatTreat.htm

After I cast my last batch three months ago, I decided to heat treat several of my bullets and test them for hardness. Below is my data, which I hope might be of some use.

Oven used was a GE kitchen oven on the standard (non-convection) bake setting. No attempt was made to determine whether the temperature shown by the digital thermometer was accurate, I just assumed it was.

Bullets were made out of two different alloys: one set were wheelweights, one set were with a 2:1 alloy of 2 parts antimonial lead to 1 part 25:1 alloy.

Hardness was tested on an ST Machining hardness tester. For those who may not be familiar with it, a bullet or ingot is placed into the tester, and a hardened point is pressed into the nose or flat part of the bullet. After the point touches the nose, the screw on which the point sits is screwed one full turn to push the point into the bullet. This causes the bullet base, which is set on a bolt within a spring, to compress the spring. The readout on the dial gauge is supposed to correspond to various hardness levels. The more the spring compresses, the harder the bullet is. You can see what the machine looks like here: http://cowboybullets.com/Lead-Tester_p_57.html

According to ST Machining, the following readings match up to hardness:

.030"-.035" - BHN 5
.043"-.048" - BHN 6
.051"-.056" - BHN 7
.057"-.060" - BHN 8
.068"-.072" - BHN 10
.072"-.075" - BHN 11
.084"-.088" - BHN 13
.089"-.092" - BHN 17-19
.093"+ - BHN 30+

My goal was to replicate the hardness of Cast Performance and Beartooth Bullets. Their bullets that I have on hand are probably about 5 years old at this point, and measured a spring compression of between .093" and .096" in the bullets sampled, so that was my goal.

The 2:1 alloy bullets had been cast and air cooled about 3 years previously. The wheelweight bullets were freshly cast. Initial spring compression of the wheelweight bullets was .061". Initial spring compression of the 2:1 bullets was .073".

The 2:1 bullets heat treated were from the the Lee 501-440 mold. The wheelweight bullets were mostly from the Lee 452-300 mold, with one group of various pistol bullets heat treated with NOE 360-180 and MiHec 9mm Makarov.

Bullets were placed standing right side up in a cookie pan and placed in the oven once the oven had reached the desired indicated temperature. Bullets were left in the oven for 1.5 hours, then removed and immediately quenched in a 5 gallon bucket of room temperature water. The pistol bullets were the first batch, heat treated at 450F. The 501-440 and 452-300 bullets were heated at 375F, 400F, 420F, 460F, and 480F. The bullets treated at 480F had a noticeable dark bronze discoloration on the exterior.

Hardness after heat treating was tested after 1 day, 2 days, 1 week, 2 weeks, 1 month, 2 months, and 3 months. Data from the 2 month reading was lost in a recent hard drive crash. I plan to follow up with readings at 6 months, 1 year, and 2 years, and have enough bullets that I may also be able to follow up again at 3 years, 4 years, and 5 years. Without further ado, on to the data.

Alloy Type     Heat Temp     1 Day     2 Day     1 Week     2 Week     1 Month     3 Month
WW             375F          .073"     .080"      .078"     .081"       .084"     .081" - Lee 452-300
WW             400F          .079"     .085"      .089"     .090"       .090"     .089" - Lee 452-300
WW             420F          .091"     .093"      .094"     .094"       .094"     .093" - Lee 452-300
WW             450F          .094"     .093"      .096"     .093"       .095"     .095" - Various Pistol Bullets
WW             460F          .095"     .096"      .097"     .096"       .095"     .095" - Lee 452-300
WW             480F          .095"     .094"      .096"     .096"       .094"     .097" - Lee 452-300

2:1            375F          .073"     .073"      .081"     .084"       .081"     .085" - Lee 501-440
2:1            400F          .076"     .083"      .087"     .088"       .089"     .091" - Lee 501-440
2:1            420F          .087"     .091"      .092"     .093"       .092"     .092" - Lee 501-440
2:1            460F          .096"     .095"      .097"     .097"       .098"     .097" - Lee 501-440
2:1            480F          .096"     .098"      .096"     .098"       .096"     .098" - Lee 501-440

WW             000F          .068"     .068"      .068"     .066"       .072"     .070" - Lee 452-300, control group, air cooled, non-heat treated

As you can see, it appears that the higher the heat treat temperature, the harder the bullets get and the quicker they harden. But all bullets hardened over time, even those only air cooled. It will be interesting to see down the road a few years whether some of these heat treated bullets soften significantly or not. Right now it seems as though the difference between 450, 460, and 480 is negligible, and even 420 may provide sufficient hardness with these alloys.

[waksupi]

I did the same testing some years ago. I also found you could pretty much pick your hardness by varying the temperature.