Took the K31 out with the
correct cartridges recently. 24.0 grains of IMR 4198 with a 130-grain cast plain-base bullet. First three shots at 50 yds within 1.5 inches; then six, eight and ten-inch groups, if I could dignify them with that term at 50 yards.
Plus, the additional new knowledge that the load apparently isn't high pressure enough to prevent blow-back through the bolt. Had a nice black soot streak down my cheek by the time I was done.
So, is it the barrel or is it the load? A quick way to find out is switch back to milspec loads, or close to them if the originals are unavailable (or too damn expensive). So a load consisting of 37.8 grains of H4895 topped with a Winchester 147 grain FMJBT was whipped up yesterday and taken to the range.
This time, groups averaged 3-4 inches, usual due to one flyer adding an inch to the groups. At this point I'm sure it's me, due to my bifocals: first that I'm old enough to need them, with all that entails about my vision and secondly, this is the worst pair of glasses I can recall having as far as useful percentage of lens. Won't be going back to the vendor for the next pair.
Regardless, I can see the barrel is fine as military surplus goes; the most recent load is mild to shoot (at least wearing a sweatshirt and Carhart jacket) and easy to make. Think I'll load up another batch of these and do some 100 yard shooting in a weekend or two.