Herter's 6mm brass
Herter's did business back in the 60's in the dark ages where you could order a rifle, barrelled action or action through the mail without an FFL. They sold a lot of stuff through their catalog including a pretty complete line or reloading equipment and components. Their catalog was a lot of fun to read, with everything in there claiming to be the best out there. In truth, the quality of most things was on the lower end of the scale, but the price was right and service was prompt. Most of their products were of some other manufacture with their name on it, but made to sell at a bargain price.
If I had the brass, I would mike the necks to check concentricity and work up loads cautiously in deference to the age and unknown quality of the brass.