Houts...Now you're making ME feel old...<<grin>>...

A gun made in the 60s can be considered "modern"...

"Older" guns would be guns made mostly prior to 1920, with damascus or twist steel barrels, or chambers shorter than 2 3/4"....

You should be able to shoot any current factory loads safely in your Fox Model B as long as they are the proper gauge and chamber length..

One consideration...Many guns made prior to the implementation of steel shot laws ( pre 1970 or thereabouts) were made with thinner walled barrels...It's not recommended to shoot them with steel shot..It's not a safety matter, but steel shot can cause a bulge in the choke area of some of the guns that were manufactured before steel shot became mandatory...This can negatively affect the value of the firearm...