Hello Mr. Kawshik,
My most emphatic congratulations for your new RIFLE and CARTRIDGE!
The 7x57 was my first, and for many years my only, big game rifle. Since 1972. It was, is as I still have and use it, a DWM Original Spòrting rifle, 1893 Mauser Action. A kind of Type C model. It came to my from my great grand father! Still in its original blueing. My second 7x57 is another Mauser action 1935.
I started to reload for the 7x57 around 1974.
To make it short, I agree with the recommendations given to you about the NORMA Oryx 156 grs bullet-cartridge brand. Their cases are one of the best for reloading. Period. Actually I think there are no better options for general big game the kind of sambar deer, wild boar and so. If you will reload and if you can find them, a Hornady Interlock or Interbond in 154 or 162 grs would be another perfect combination. And relatively not too expensive.
Reloading the 7x57 is a pleasure! Very easy to obtain excelent result with almost any medium-medium slow powders. Any of the 4350 would be, to me, one of the very good powders for 150 to 160 grs bullets.
About your rifle, well, I cannot say nothing other than CONGRATULATIONS!! I have two BRNO ZKK of the same configuration and period as yours: A 601 in 308 Win and a 600 in 9,3x62. I am searching for the last 30 years for one exactly like yours, a ZKK 600 in 7x57!! I miss for ONE DAY a beautiful ZG47 in 7mm Mauser....I am still kicking in my head....
My best wishes for you !!
C F