Kroil would very likely work. Or you can try a 50/50 mix of acetone and ATF. Lots of folks who do machine tool restoration use that. Put it in a container with a lid that won't melt from the acetone, shake it real well, and then pour it on, or submerge the action in it for a few minutes, then pull it out, wait a bit, and try to break it loose. Acetone acts as a carrier for the oil, and then evaporates, leaving the oil behind. PB blaster would probably work, too, but it may damage the bluing. If you're not planning on refinishing the action or barrel, stay away from it.