I'm sorry, I didn't realize that shot buffer/ filler was left out in the third edition of my book.
I really like using it, and don't believe it matters too much which brand is used. Grex is no longer available, but Precision Reloading offers more than one variety, and I believe you can locate them on the web with that name. I tried all their they offer and all worked equally well for me.
Some other things that work great for filler are cream of wheat, cornmeal, and hominy grits. All these are hydroscopic, meaning they absorb water from damp atmospheres. I'd advise drying them in an oven at 125 deg for a couple hours before using. None of these compress as easily as shot buffer.
You'll find fillered loads very nice when shooting bullets cut for gas checks without the checks, with lower velocity loads than if checks were used, but higher than if not fillered. It's a cheap way to shoot with decent power.
The reason fillers stop leading is because they mop the bore and sweep it clean while the lead is still molten. Competition shooters generally danm it saying it hurts accuracy. However, I have found it does only when too much is used, in which case the wad upon exiting the bore goes out of square as it blows off the bullet, which equals an out of square bullet base. I like to find a powder which fills the case of interest to within perhaps a half inch of the bullet base, then add enough filler so it compresses firmly when the bullet is seated. The stuff is really easy to compress, so normally the case can be just filled to the top and wiped off.
Compression always improves powder ignition, and smooths out the push against the bullet, which means good accurate loads can be worked up quite a bit hoter than without filler, and hot weather has less bad effect, or non, on performance.
