johnly
01-08-2009, 03:16 PM
I have a Marlin 336 in 219 Zipper that I want to develop a cast bullet load for. Small bore microgroove barrels combined with a centerfire cartridge have a history of eroding barrels pretty quickly with jacketed bullets. Not a nice thing to do a rifle that only had a lifetime production of run of only 3200 units.
I located an out of production DC Lyman 225462 GC mold for the rifle, as I wanted a heavier bullet with a long bearing surface to help address the challenges of the microgroove barrel. I cleaned the mold, then applied drop-out, pre-heated it, then started casting bullets with a 10:1 alloy. The bullets filled nicely, but the mold didn't want to drop the bullets from the cavity without several stiff raps of my sprue cutting stick and it was clear that the hang up was in the area of the bullet base. After casting a handful of bullets, I decided enough was enough, and turned off the pot and let the mold cool. Looking at the GC shank, small indents in the bullet base near the parting line were visible. Sure enough, when the mold cooled enough to handle one could see where the mold corners were dinged in this area.
The defects were pretty small, but then again so were the bullets. My first thought was to remove the burrs with some diamond paper wrapped on a length of drill rod. I didn't really like the idea and the displaced metal came from some where where it should have been in the first place. Then I had the idea of using a press and pin gauges to move the burr material to where it belonged. I started out with a 0.198" pin inserted about 0.050" into each cavity and applied pressure. I kept on increasing the pin diameter until I matched the nominal diameter of the gas check shank area of a cast bullet. In this mold that was .213". The next evening, I turned on the pot, I cleaned the mold, re-applied drop out, pre-heated the mold, and started casting. The difference was immediately noticeable. The bullets were cleanly filled out as before, but now they easily dropped from the mold. In cases where they didn't just drop out when the mold was opened, half the time they would be in the left side of the mold and the others would be in the right. Success!! I must have cast close to 400 bullets nice looking bullets over the next 90 minutes.
Just though I'd pass this tip along should anyone else be in similar circumstances.
John
I located an out of production DC Lyman 225462 GC mold for the rifle, as I wanted a heavier bullet with a long bearing surface to help address the challenges of the microgroove barrel. I cleaned the mold, then applied drop-out, pre-heated it, then started casting bullets with a 10:1 alloy. The bullets filled nicely, but the mold didn't want to drop the bullets from the cavity without several stiff raps of my sprue cutting stick and it was clear that the hang up was in the area of the bullet base. After casting a handful of bullets, I decided enough was enough, and turned off the pot and let the mold cool. Looking at the GC shank, small indents in the bullet base near the parting line were visible. Sure enough, when the mold cooled enough to handle one could see where the mold corners were dinged in this area.
The defects were pretty small, but then again so were the bullets. My first thought was to remove the burrs with some diamond paper wrapped on a length of drill rod. I didn't really like the idea and the displaced metal came from some where where it should have been in the first place. Then I had the idea of using a press and pin gauges to move the burr material to where it belonged. I started out with a 0.198" pin inserted about 0.050" into each cavity and applied pressure. I kept on increasing the pin diameter until I matched the nominal diameter of the gas check shank area of a cast bullet. In this mold that was .213". The next evening, I turned on the pot, I cleaned the mold, re-applied drop out, pre-heated the mold, and started casting. The difference was immediately noticeable. The bullets were cleanly filled out as before, but now they easily dropped from the mold. In cases where they didn't just drop out when the mold was opened, half the time they would be in the left side of the mold and the others would be in the right. Success!! I must have cast close to 400 bullets nice looking bullets over the next 90 minutes.
Just though I'd pass this tip along should anyone else be in similar circumstances.
John