The reason it does not look like gas cutting to me is primer leakage gas cutting will be around the firing pin hole,where the gas is jetting past the primer.
Those "pits" are located out near the rim diameter.
I cannot see any gas getting to that location still carrying the heat and pressure to cut.
I don't think its gas cutting.I don't think its about the primer.
The rims of those cases look torn up. The beat up rims are at the right diameter to match the dents in the breech face.
You get to be the one to play detective.I don't have the gun to look at.
I suppose a bit of contamination could have embedded in the brass.
But there is something else. Solids are not compressible. I spent a career building and running plastic injection molds.These were mostly developmental molds. The steel was "pre-hard". It was roughly a 4140 alloy,semi-hard,but machinable with high speed.
The parting line ,where the mold halves separated,would start out surface ground flat.Pristine! Beautiful!!
But if flakes came off the sub gate break,or of wet material caused nozzle drool,or if for any other reason bits of nylon or Delrin or Lexan or any other plastic remained on the plates when the mold press clamped up,
That plastic would be pressed into the steel and it would displace the steel.
The plastic is mallable,but its not compressable.
If the mold was made poorly,and ran dirty, some parting lines literally looked like they had been worked over with a hammer.
That beat up brass may be impressing into the steel. The high spots focus all the force on a very small area.
There is something else that could aggravate the situation.I know nothing about how Ruger makes those slides.I doubt they are machined of bar stock.
Ruger has been an innovator of production methods. No one is better at investment casting.
IMO.its possible that slide or breech face is a powdered metal.sintered part.
Pressed and baked like a cookie.I'm not saying it is,but modern manfacturing methods are a fact.
Looking at your breech,zoomed up,those are dents,not gas cuts,IMO