I just took it by the lgs and after comparing many others we were surprised to find its not a crack. Oh well, the gun is reliable as can be and accurate to boot. I think I'll start calling it a tactical cast mark.
Whether it's a crack or not, that piece that is suspect of being cracked is cheap and easily replaced. Send Ruger a photo of it and they will more than likely send you a new one at no cost.
I have two MKIIs and several spare recoil spring assemblies. They all have similar marks like that. I think that's just from when the part was cookie cutter'd off the sheet. I wouldn't give it any thought. You're going to have replace that spring any way in a few hundred bricks.
That part is blanked (stamped) out of sheet steel; that line is a mark from the manufacturing process. And it is not in the bolt, it is part of the recoil spring assembly.
It's not cracked. Just looks like rough edging. Mine's similar and i've since shot countless bricks with no affects on any functioning. Shouldn't be concerned unless it was affecting functioning
I hit mine on a scotcbright wheel and polished it. Take out the recoil spring assemble and stop by any machine shop. They should be able to hit it on the wheel for a couple bucks. If your in S NJ Ill gladly do it for a cup of coffee.