Clutch, I have a Lyman 575213A Old Style mold and I can give you the dimensions for it's plug if that will help.
The overall diameter of the plug is .579 which may be a little different for yours.
The diameter of the part that forms the cavity is at the base: .425. Subtracting this from the overall diameter equals .154, making the thickness of the skirt .077.
The depth of the cavity is .360. It is cone shaped. The top of the cone is .145 wide.
A couple of years ago I turned one of my own style for this mold, making the skirt thinner and the cavity deeper so as to expand better with light charges. It works well enough, but I believe I made the cavity a little too deep for optimum stability.
The part that forms the cavity is .435 at the base and .325 at the top and is .410 in length. I believe it would work better if the length was left the same as the original. With this one, the skirt thickness is .072.
This plug makes bullets that will still hold up well with the service charge, but will also expand very well with very light charges. However, I believe the longer cavity throws the center of gravity too far forward. I've noticed more keyholing at ranges as close as 25 yds and out to 100. One of these days I may turn another one with the only difference between it and the original being the skirt thickness by changing the angle of the cone.
If the plug hole in your mold is different than mine (it shouldn't be more than a couple of thousandths), you can easily add/subtract the difference and come up with the same skirt/cone dimensions.
Hope this helps!
