Lyman sizer

[james nicholson]

Just an observation, question about this sizer. The rod in the center of the die, which I am calling the seal rod, is concave on the top and flat on the bottom, at least the two new ones I just bought are. I would think to better seat a gas check, the rod should be flat on the top and concave on the bottom. Does anyone know about this? I had never noticed this before, but when I bought a used one from ebay, it was so gunked up with hardened lube, I had to boil it out. While playing with it, the seal rod fell out and I started thinking about how to put it back in, seemed the flat end should go up, but the new ones, in their unopened packages, are concave end up.

[JonB_in_Glencoe]

the seal rod (as you call it) is known as a Punch (Part I).
http://castboolits.gunloads.com/showthread.php?34525-manual-for-a-Lyman-45&p=2670223&viewfull=1#post2670223

To your question: It shouldn't matter, unless you have a sprue protruding out the bottom of your boolit, then you'd want the concave side against the GC.

[Larry Gibson]

The two together are referred to as the "H&I" die. This is because on Lyman schematic drawings for the 45, 450 and 4500 that is the alpha Identifier given for each part.

The "sizer" is the "H" die and the "punch" is the I "punch" part.

With older Lyman slip on GCs the flat part was up. However, it was found years ago it was better to have the concave portion up as it keeps lube from going between the I and GC, especially with newer crimp on GCs which slightly bow out as they are crimped (depending on how much crimp).

I have the concave end up in all my H&I dies regardless of whether I use crimp on GCs, older Lyman slip on GC or my own home made GCs which are slip ons.

Larry Gibson