Water Dropping?
I've been reading about increasing the hardness of cast bullets by dropping them from the mold into water. I have also been reading about testing the hardness of bullets with a set of artists pencils.
I watched a YouTube the other day of a guy casting bullets and water dropping them. He made a few air cooled as well. He tested the hardness with his finger nail and came to the conclusion that water dropping and air cooled were the same hardness.
So, I tried it for myself. I tested the hardness of my air cooled cast bullets with pencils. I then cast a few bullets and dropped them into water. After about a hour I tested the water dropped bullets with pencils. Sure enough they tested the same as the air cooled bullets
Whats up with this? Do these bullets have to sit and cure for awhile before then become harder? If so How long should they sit before I test them for hardness?
Thanks
Steve
QuoteDo these bullets have to sit and cure for awhile before then become harder? If so How long should they sit before I test them for hardness?
yes, well "cure" isnt the precise term, I think its called "grain growth" or something but more or less.
you should see most of the hardening after about 48 hours and and they will continue to harden for a few weeks
In order to harden from quenching a couple of things have to happen. One alloy related, and one environmental.
First, the alloy you are casting from must contain antimony or another grain refiner. Pure lead and lead tin alloys are not susceptible to quench hardening. Clip on WW alloy and isotope lead both harden readily.
Second, the bullet must be near the "slump" temp when it hits the water. Unless you aggressively cut your sprues as soon as they are cool enough to not tear, the bullet may be cool enough to not harden a huge amount. I would say about 15%-20% of the bullets I drop have a sprue that is slightly torn.
There should be measurable hardening immediately after casting, but it will usually change over time. Generally they will harden for the first couple of weeks, with 90% of the hardening in the first 24-48 hours. If sizing it is best to size them as soon after casting as possible. Sizing the next day will be noticeably more difficult.
A few years back I helped my son do some extensive testing on heat treating lead alloys. The methodology and results are posted here: http://fellingfamily.net/isolead
For a more scholarly explanation read here:
http://www.lasc.us/HeatTreat.htm
Incidentally, I saved my sons samples and re-tested them 24 months later. I found all the non-quenched bullets had continued to harden towards a bhn of 14, and all the quenched ones had migrated towards a BHN of 22-24. I say migrated for the quenched because the very hardest groups were harder than that after 24 hours, but two years later had softened some. One group dropped from a BHN average for 10 sample of 32 to 24 after two years.
This has lead me to believe that most alloys have a "desired" metal matrix and corresponding hardness. The molecules will continue to migrate towards that matrix over time. For the best long term results, tests could be conducted to predict what the hardness of these ideal matrices are, and then a quenching process select that will place the alloy in that state. The result would be a bullet that would not change significantly in storage even over a hard time.
For instance, the bullets from series 2, were water dropped after casting froma 650 degree pot. They averaged 25.88 the next day, and averaged 24 two years later. And series 16, which was air-cooled, then heat treated in the oven at 450 and quenched. These measured 24.87 after one day, and 23.39 after two years. Either of these seem like they would be candidates for a great method for my allow as they are quite stable over time. The second method would be even more so as you could size before oven treatment, ensuring the resultant bullets were not work softened at all after the heat treatment.
Hope this helps.