I have a couple. Very accurate, extremely well made and the straight pull bolt is fast and smooth. Cool factor is pretty high too…..
Surplus GP11 ammo is not as available as it used to be, but AIM surplus and Midway has it every now and then. Modern ammo is available, just not as cheap.
If you can find a nice, numbers matching example with a decent stock, I’d say go for it. You have to be careful though...after the K31 you're going to want a 1911 rifle and K11 carbine!
