This is only my second post since joining and NitroX suggested that I try a question here so if I'm going to get flogged for it, so be it.

For more decades than I want to remember I have had a BSA 458 Win. Mag.
I have never known exactly what model it is because it has no mention of same anywhere on the gun.
On the left side of the chamber is stamped ' 69 GRs.nc 510 GRs. bullet '.
Would anyone know what model it is and also what the writing describes ?
It has a single blade fixed rear sight... now would the writing describe a load that the factory made the sights on the gun for, or is it a proof load of sorts ?
And what do the small letters 'nc' denote.

I do know some BSA variations had the model name on the gun as in Majestic, but I also have another BSA in 7X57 that simply has ' BSA 7X57' stamped on the side of the receiver, this is probably a Hunter model.

Any help will be greatly appreciated.