3
358156hp
Guest
My alloys are composed mostly of scrap, to which I add other alloys to achieve my desired performance. At this point I'm mixing range scrap, a bit of lino of uncertain origin (could also be monotype), and tin, in the form of 95/5 lead free solder (95% tin, 5% antimony. The real wild cards are the range scrap and the lino. Many people call the single character type pieces "linotype" but my understanding is that they should actually be monotype. Please correct me if I'm wrong.
My goal for these particular bullets is 13-14 bhn, air cooled. They are 357 mag. hollowpoints that should leave the barrel at slightly over 1200 FPS. They will be tested for brittleness and expansion before going into service.
I cast perhaps 50 bullets with this alloy last night from a new mould, and promptly remelted them all because it was a new mould, and I was still getting wrinkling which I accredited to the new mould "breaking in". I've seen this a lot with new aluminum moulds and don't consider it to be an issue. It's just a break in thing. The PID was set at 400C, which is slightly over 750F.
After the mould warmed up properly, I noticed the alloy seemed to "freeze" rather abruptly, and this continued through out the session. I did experiment with watching the PID display fall and rise when the bullets were returned to the melt, but for the major portion of the session, my pot temps fluctuated less than ten degrees. Still the rather abrupt sprue freezing continued. My first thought was that this batch of range scrap may have a bit more antimony than the last one, so I poured two ingots to test later. Finally, I cleaned everything up, and shut it down. The bullet bases were slightly frosted at this point. I normally cool them with a damp cloth at this point to speed up sprue freeze while allowing the noses to continue building up heat. The sprues broke cleanly and freely without much tearing.
This morning I tested the ingots in my LBT hardness tester, and they came out at 13 bhn. Since they're ingots, and cool slower than bullets will, I estimate bullet hardness will be 14-15, air cooled. What puzzles me is the really rapid freezing of the sprues, and that the surface of the alloy in the pot "cracked" when it froze. I'm sure you've seen this before too, and there has to be some sort of correlation between the fast, hard sprue freezing, which suggests to me a high antimony and/or arsenic level, and the surface cracks in the cooled pot. I seem to be getting high alloy shrinkage, which I have never investigated it before.
Plan B will likely include adding more soft lead to the mix, but that kind of flies in the face of my BHN being on target. One other observation I neglected to mention, I suspect this alloy is probably a bit rich in tin, it has that really bright, light color to it that I first noticed ages ago when I misplaced a decimal point in my cyphering and ended up with about 20% tin in an alloy. It sure was purty though.
What do you think I'm seeing here?
My goal for these particular bullets is 13-14 bhn, air cooled. They are 357 mag. hollowpoints that should leave the barrel at slightly over 1200 FPS. They will be tested for brittleness and expansion before going into service.
I cast perhaps 50 bullets with this alloy last night from a new mould, and promptly remelted them all because it was a new mould, and I was still getting wrinkling which I accredited to the new mould "breaking in". I've seen this a lot with new aluminum moulds and don't consider it to be an issue. It's just a break in thing. The PID was set at 400C, which is slightly over 750F.
After the mould warmed up properly, I noticed the alloy seemed to "freeze" rather abruptly, and this continued through out the session. I did experiment with watching the PID display fall and rise when the bullets were returned to the melt, but for the major portion of the session, my pot temps fluctuated less than ten degrees. Still the rather abrupt sprue freezing continued. My first thought was that this batch of range scrap may have a bit more antimony than the last one, so I poured two ingots to test later. Finally, I cleaned everything up, and shut it down. The bullet bases were slightly frosted at this point. I normally cool them with a damp cloth at this point to speed up sprue freeze while allowing the noses to continue building up heat. The sprues broke cleanly and freely without much tearing.
This morning I tested the ingots in my LBT hardness tester, and they came out at 13 bhn. Since they're ingots, and cool slower than bullets will, I estimate bullet hardness will be 14-15, air cooled. What puzzles me is the really rapid freezing of the sprues, and that the surface of the alloy in the pot "cracked" when it froze. I'm sure you've seen this before too, and there has to be some sort of correlation between the fast, hard sprue freezing, which suggests to me a high antimony and/or arsenic level, and the surface cracks in the cooled pot. I seem to be getting high alloy shrinkage, which I have never investigated it before.
Plan B will likely include adding more soft lead to the mix, but that kind of flies in the face of my BHN being on target. One other observation I neglected to mention, I suspect this alloy is probably a bit rich in tin, it has that really bright, light color to it that I first noticed ages ago when I misplaced a decimal point in my cyphering and ended up with about 20% tin in an alloy. It sure was purty though.
What do you think I'm seeing here?
