What are the composition of these flat base bullets?
Wheel weights air cooled?
Wheel weight water quenched?
Hard cast?
The alloy of cast bullets is not as critical as a lot of people think.
All of the bullets referred to in my article would be wheel weights from about twenty years ago. I dropped them from the mold into water, just for the convenience of it. Like not damaging them when they drop. As we know, dropping them into water only makes them harder for a short while, then they revert to the original hardness of the metal.
When I was seeing how fast I could accurately drive cast bullets in a 30-06, I usually used pure linotype with a gas check. When I was doing this experimenting, I accidentally discovered a very significant fact about shooting cast bullets, something that I have never heard of, or read of, anywhere.
I was doing this in the winter time at a virually unused range, with lots of snow on the ground. In the spring I could pick up my bullets, completely undamaged, from stopping in the snow.
This testing was being done at a time when ordinary shooters couldn't even dream of having a chronograph. I would take one type of powder and load in groups of five, going up a couple grains with each group. Then I would shoot them in the groups of five, for accuracy. With cast bullets they go from being quite accurate, to one or two foot flyers, just with the addition of a bit more powder.
In the spring of the year when I recovered my bullets, I discovered that some, obviously the bad fliers, had a groove cut down the side of the bullet, full length of the bullet and about 1/16 inch across!
It was plain that even a linotype bullet with a gas check, could not hold the pressure, so it just cut a swath down the bullet to escape.
As a point of interest, to get highest velocities, I figured slower burning powders had to be used. Thus, I used quite a variety of slower burning rifle powders. I had the original Lyman Cast bullet loading guide to go by, but figured for best velocity and accuracy I would experiment further than what the Lyman book showed. Thus, I used a wide variety of powders not usually shown for cast bullets.
Don't want to stir the pot here, just reporting, but one of the powders that gave the best accuracy, and a powder I used a lot, was good old war surplus H4831, loaded down to about 75% or so, of normal loadings!