I think I've got a SQUIB!!!

[BEARMAN]

Say, the action on my Sig locked up solid, and the primer on the case, when I finally got it out of the chamber, was sitting proud.

High pressure due to the squib?

Anything I should look out for? I don't see any visible damage.

The reason the primer set back, is because there was no powder, the case did not set back against the breech face and hold the primer in place. This happens a lot in very light loads in revolvers. The primer ignites the powder but the load is so light the case does not set back so the primer backs out a thou or so and interfers with the rotation of the cylinder, a little heavier load in revolvers usually stops this. In either case it is not a sign of pressure.