bradsoto
07-14-2017, 04:36 AM
Hello and thanks for the wealth of information. This is my first post.
I wanted a lead-free casting alloy to get around some laws here in Canada. Of course I started with bismuth-tin, and ended up nowhere. The problems with bismuth-tin are (among others):
low melting point (cant powder coat, lots of fouling)
expansive (sticks in the mold, frustrating as hell)
So I needed to find an alloy that contracts with a higher melting point than bismuth. I alloyed bismuth with zinc. Around 10-16% zinc is the sweet spot, you dont have to bang your mold all day at 10% (minimal expansion) and 16% is the isostatic (no expansion or contraction) eutectic.
199637
Here is what they look like cast. The larger bullet is 210 grains and the smaller is 105. I designed a subsonic bullet shape over at Accurate Molds (this was my first design for tumble lubing bismuth-tin boolits)
http://www.accuratemolds.com/bullet_detail.php?bullet=31-252S-D.png
http://www.accuratemolds.com/bullet_detail.php?bullet=31-126S-D.png
199638
It's malleable too. Here is a bullet after being chewed on
199639
Next I did the old hammer test. Right away I knew the bullet would be fragmenting
199640
The melt temp of this alloy is higher than powder-coatings. So I coated them and did some test shots. No fouling! Finally I whipped up some ballistic jello in a 4L milk jug to see what would happen with terminal ballistics. The straight through shot is the 210 grain bullet at <mach1 and the perfect expansion shot is the 105 grain at <mach2. This pic is 3D like the old "magic eye" books, just line up the white dots by crossing your eyes and you can see depth.
199641
Where can this go next? I'm making this post because I have to take a break from boolits and I'm hoping someone will take over. To get immediate expansion at subsonic velocities either the meplat has to be bigger, hollow, or we'll have to cut and X down the nose. I already designed a better subsonic bullet with a larger meplat and a 1-caliber long boat tail over at Accurate Molds. The bullet is in the mold upside-down. When the bullet is subsonic the shape of the tail is most important to get right :) :
http://www.accuratemolds.com/bullet_detail.php?bullet=31-242S-D.png
http://www.accuratemolds.com/bullet_detail.php?bullet=31-121S-D.png
How fast can this alloy go before we get too much fouling? I don't own a chronograph :( . Maybe there is another high-contracting, high-temp metal that makes a better alloy with bismuth for cast boolits? I can cast this alloy heavier and cheaper than buying copper bullets... now you can too! :drinks:
I wanted a lead-free casting alloy to get around some laws here in Canada. Of course I started with bismuth-tin, and ended up nowhere. The problems with bismuth-tin are (among others):
low melting point (cant powder coat, lots of fouling)
expansive (sticks in the mold, frustrating as hell)
So I needed to find an alloy that contracts with a higher melting point than bismuth. I alloyed bismuth with zinc. Around 10-16% zinc is the sweet spot, you dont have to bang your mold all day at 10% (minimal expansion) and 16% is the isostatic (no expansion or contraction) eutectic.
199637
Here is what they look like cast. The larger bullet is 210 grains and the smaller is 105. I designed a subsonic bullet shape over at Accurate Molds (this was my first design for tumble lubing bismuth-tin boolits)
http://www.accuratemolds.com/bullet_detail.php?bullet=31-252S-D.png
http://www.accuratemolds.com/bullet_detail.php?bullet=31-126S-D.png
199638
It's malleable too. Here is a bullet after being chewed on
199639
Next I did the old hammer test. Right away I knew the bullet would be fragmenting
199640
The melt temp of this alloy is higher than powder-coatings. So I coated them and did some test shots. No fouling! Finally I whipped up some ballistic jello in a 4L milk jug to see what would happen with terminal ballistics. The straight through shot is the 210 grain bullet at <mach1 and the perfect expansion shot is the 105 grain at <mach2. This pic is 3D like the old "magic eye" books, just line up the white dots by crossing your eyes and you can see depth.
199641
Where can this go next? I'm making this post because I have to take a break from boolits and I'm hoping someone will take over. To get immediate expansion at subsonic velocities either the meplat has to be bigger, hollow, or we'll have to cut and X down the nose. I already designed a better subsonic bullet with a larger meplat and a 1-caliber long boat tail over at Accurate Molds. The bullet is in the mold upside-down. When the bullet is subsonic the shape of the tail is most important to get right :) :
http://www.accuratemolds.com/bullet_detail.php?bullet=31-242S-D.png
http://www.accuratemolds.com/bullet_detail.php?bullet=31-121S-D.png
How fast can this alloy go before we get too much fouling? I don't own a chronograph :( . Maybe there is another high-contracting, high-temp metal that makes a better alloy with bismuth for cast boolits? I can cast this alloy heavier and cheaper than buying copper bullets... now you can too! :drinks: