I bought a K31 with a matching s/n bayonet from AIM, for $300. I've got to say I've been happier with this purchase than almost any other firearm I've bought in the last couple of years.
The mechanicals are in excellent condition, with good bluing, very little wear evident, and a nice, shiny bore that passes the muzzle test with flying colors. The bayonet is beautiful, and the issue documentation under the buttplate is just plain cool. Disassembling the rifle really made me think: "Swiss Watch." Excellent 2-stage trigger on this gun.
The only problem I had was that my 50 year-old eyes simply can't see the iron sights. The rear sight is just a blur, and after my first range session (where I was barely able to shoot at 25 yards) I resolved to put a scope on it.
I didn't want to drill and tap, so I looked at offset scope mounts, diopters, and a nifty little scout mount that I ended up purchasing. I put a 2.75X Burris Scout Scope on the gun, and went out to the range this past weekend. I sighted everything in at 50 yards, and was quite pleased with the 1/2" to 3/4" groups I was getting. I needed 8 clicks down and 8 clicks left to zero the reticle - a testament to the quality of the scout mount, which, by the way, has elevation and windage adjustments built into it.
Here's the mount I used. The manufacturer makes mounts for several different surplus rifles. He also sells rings and scopes (but the scopes are the cheap NCStar stuff, which I had no interest in.)
And the scope. I thought about getting a handgun scope, but honestly, I don't believe the eye relief would work. The Burris is just at the edge of having enough eye relief, and it's designed to be a scout scope.
I was a bit concerned that the 2.75X wouldn't be useful at 100 yards, but as long as I use a circular target with some contrast, I had no problem seeing clearly. Also a bit of a concern was the description of the reticle: Heavy Plex. I looked up the specs, and at 100 yards the fine part of the reticle subtends .71 inches - better than I can resolve at that distance. No worries, the reticle is great. I am completely confident that I could take a deer, or an elk, at 200-250 yards with this combo.
Here are some pics. I know I can get my 100 yard groups down to 1-2 MOA. This gun can shoot those kinds of groups quite easily, I'm sure.
I urge anyone who is on the fence about this gun to buy one before they are gone. Great gun, at a great price.
Oh yeah, one more thing. As I was firing the gun, I would eject the round and catch it out of the air. Normally, I would 'hot potato' the brass for a while, letting it cool before looking at it. No need with this gun. It was really strange. A freshly fired and ejected case was barely warm to the touch. I don't know why, but it was pretty neat.