PB Blaster and Kroil are both good at cutting rust. WD40 does nothing to rust except make it wet. I restore old Jeeps ('40s era) so I am very familiar with rust (even in Seattle).
![Big Grin](https://smith-wessonforum.com/images/smilies/biggrin.gif)
But as others have said, that doesn't look that bad, as long as the face of the bolt is clean, the bolt locks into place, and the bore is free of obstructions, shoot it.