Thanks for the input, gents.
Jim, my Lyman gas checks are probably 35 years old. I think I bought the Hornady GCs in about 2006 or so. There is a pronounced visible difference in color, and the rim of the Hornady GCs are a little bit thicker at the edge as I would expect based on marketing material I have seen (or maybe a magazine article).
Looking at an image of gas checks on Lyman's website, they do appear to have a thicker edge than they used to, and look a lot like Hornady gas checks. I noticed there is no longer a Lyman .41 caliber gas check offered. I have some Hornady .416"s to use for .41 mag casting because someone told me a long time ago the .416s would work. If it doesn't, I guess I'll retire my 410610 mold and just cast the RCBS .41-210-SWC. I kinda want to get away from using gas checks anyway and I'm trying to use them up. I have about 4500 .357 and about 1800 .41s to be used up.
