I've got a Lyman .410 Snover single cavity mold I bought used (ebay). Before use, I cleaned it with brake cleaner and a nylon brush, and it appeared to mate/close perfectly with no gaps. During my first use, it began to stop closing cleanly. I could feel the pins sticking when opening it, and the top and bottom would rock/pivot on the center.
I scraped away any visible lead with a chopstick while it was still hot, and cleaned it again after it was cool. It closes better, but still not like it did before. I checked the surfaces with a precision straight-edge, and they appeared perfectly flat. Whether I have the mold on the handles or not, with or without the sprue plate attached, it still rocks a little with a small gap visible when help up to the light.
While I can't feel the pins sticking anymore, that is still the area where it pivots. Hence my question: is it possible that the pins could swell from the heat during use? Before I do something like try to relieve the inside of the pin-holes or some, I thought I'd ask if y’all have any ideas.