I’ve got a 257 Rob M70 of the same era with the yellow goo bedding compound. Mine was a 3” gun at best when I first shot it. I knew it couldn’t be that cruddy and something was afoot.
While I was at the range I slid my paper membership card along each side of the barrel noting with pencil where the binds were. After removing the stock I used my pocket knife drawing rearward carefully scraping what was mostly varnish away in a delicate smooth manner. When I reinstalled the stock I had very even space exactly a membership card thickness on each side. Shot 12 more shots and groups were around 1 1/2”. Further barrel channel inspection found the pressure point at the front underside of the barrel was actually pressing diagonally. I cut a plastic shim out of a carton and placed it under the recoil lug. This lifted the barrel enough to float the barrel without pressure. Next group was 3/4 moa. 20 more shots went under or at 1” - all at the range while folks were looking at me like I was nuts.
When I got back home I re-bedded without the shim & sealed up the channel.
My middle screw is just snug - I’ll have to try the collimating trick! Never heard of that but makes sense.
I bet yours benefits from the same kind of treatments - the barrels if that era are generally great.
