The Brno rifle will be way better than the 50 year old ammo. Fine to shoot it but a 7x57 that I used for nearly 30 years got more accurate as it got older . . . .actually I think ammo and projectiles improved heaps during this time.
Reloading will get you the best results in term of both power (US ammo is woeful in 7x57) and accuracy. 160 Gn Sierra's are very reliable on any NZ game and nearly always shoot well in just about any 7mm you can shoot them out of.
Cheers
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