If the barrel has been hitting it, it could have marred the end of the firing pin, and cause what you speak of, so check the tip of the pin to see that it is still domed in shape. The bottom firing pin, as you know, aims downward, and gravity makes it want to go down, if not for the spring. If the hole for the pin gets carbonized, from leaky primers, it can cause the spring to stick, which would allow the pin to protrude when opening and closing the barrels. Midwest has both new springs and pins listed, so I would replace both, if cleaning didn't help.