Re: PTR 91's
Got one! Scoped it and it shoots excellent. I have not quantized it except to shoot at metal target at 100, 200, 300, 400, & 500 with exellent results. My son-in-law has shot his scoped PTR-91 at metal targets at 600 & 800 yrds too with good success. That means among all our various semi-auto military guns, scoped and not scoped, high power and varmint cartridge types (223, 7.62x39), and military bolt guns, none shot as well as the PTR-91 with a scope. That includes several Garands and a M1A (but the M1A is close, very close).
This is a good, accurate gun well worth having. But as with all H&K roller lock designs that have groves in the chamber, there are limits to which ammo you can use. We found out the hard way (we didn't read the notice packed with the gun) but it only took cleaning the chamber to get the gun working perfectly. Mine has never seen surplus ammo and had zero ammo problems. My son-in-law no longer shoots surplus ammo in his PTR-91 but shoots my reloads that work fine.