I've had my k31 for well over a decade and shoot it a lot, about 200 jacketed and maybe 600+ 150gr and 200gr cast.
From the beginning it had the odd trait of shooting to the right with cast bullets. I was going to knock the front sight over but then I found it shot perfectly to the sights with jacketed bullets and service loads. I'm talking about 3 and a half inches for 150gr and 5 inches with 200gr bullets, this is at 50 metres. This is consistent no matter the load or how I'm shooting; prone with, or without, a sling or using a rest. I don't get this from any other rifle. It cannot be due to the recoil moving the point of impact sideways as I am left handed so I would expect the shots to go left if that was the case, also I would expect to see some horizontal stringing but that's not evident. The stock was putting some sideways (left side) pressure on the barrel at the fore end tip, but relieving that has made no difference.
It is now started stringing shots vertically, like 3 inches vertically whilst horizontal is just 3/4". It doing this with several different loads, including ones that I've used many times before that gave tight, round groups, just several inches to the right!
I've already checked out the Swiss rifles site and various other bulletin boards and going by posts about bedding the k31 I've tried shiming the front barrel block up and down, no difference. Shimed under the barrel at the fore end tip to apply upwards tension, no differance. Fully floating the barrel, groups opened right up. Removing the top hand guard so there is no pressure there, groups became more like a random scatter! The recoil abutment looks good, solid, even contact.
So any ideas before I move on to devcon ?
I did notice accuracy seemed to have dropped off when I last shot it with jacketed bullets. That was in May and I found afterwards the action screws had decided to wind themselves out - again!