Originally Posted by
almar
The idea is to get a certain density like 1.7 or 1.6 grams per cubic centimeter. So in other words, a given weight for a certain volume. You can control both, one with a scale and the other by measuring and putting a reference mark on your die. The pressure and application time are not constant from batch to batch or day to day or for a given humidity level so you cant rely on just that to get a consistent density. A consistent density from puck to puck and grain to grain is as desirable as consistent grain sizes.
For example, the piston i use is stepped from 3 inches in diameter at the base to 2 inches at the top. so my reference mark is when the top of the 3in. step reaches the top of the die. From there, i check how much height is left before the piston bottoms out. In my case that was 0.55 inches. I have 2 plastic disk spacers at 0.100 each so the remaining amount of space for the powder is 0.35in. Good, now i calculate the volume of that cylinder and figure out how much powder by weight i need to add in order to get 1.6g/cc, in my case that's 64 grams. Its important to not overdo the density, but the best for low velocity deviation and accuracy i believe is to be consistent from puck to puck as much as possible. I like to take a bit of extra time to make sure the powder is nice and even in the die and make sure that the ram is properly centered on the piston to ensure i get even pressure and level pucks. There is a slight learning curve, but once you figure it out, it becomes a production line.