What Briman has told you is definitely spot on. GP-11 is the $h!t for the K-31. Definitely match-grade quality ammo. As mentioned, it is expensive though. The K-31's, in my opinion, is by far the most accurate military surplus rifles that you'll find today. The Swiss never produced any corrosive ammo, unlike most everyone else. Also, you may find a tag under the buttplate with the name, unit and location of the previous Swiss soldier that "owned" the rifle when they were still being issued. Pretty interesting.