Does anyone know the size of the o-ring that fits inside the breech of the barrel of the .357 Challenger? I was watching a video of Bin inserting an o-ring there and it seems to fit into a slot inside the barrel. The one I used to replace mine that was blown out and lost when it blew up the mag months ago "fits" in the barrel but isn't quite big enough to fit into the slot I saw in the video. That may be why I have a problem loading some slugs.