Question on Old WinchesterWestern Super X 257 Roberts ammo

[Huffmanite]

Hi Folks,   I have a 1891 Argentine action 257Roberts rifle, so shooting any 257 + P  ammo in it is not recommended.   I have an  old  box of Winchester Western Super X 257 Roberts ammo with 100 gr. Silvertip Exp. bullets.  Nothing on the box to tell velocity of this ammo.  There is a code on the box (White box, large X on box with super on it)  which is   X2572.  Price tag on box is $15.70.   Presently, Winchester makes only +P 257 R ammo.  Any one know if the ammo I have is standard load 257 R which was discontinued by Winchester years ago?

[pastorp]

Huffmanite, +P ammo will be so marked on the box and the headstamp of the case on all factory loaded ammo. Byron