Are they just the plastic wadcutter bullets or just plastic cases?
I have the Speer red plastic .38 shells/cases and the black hard plastic bullets that snap in place.
What you do is push in a Magnum type primer in the case...insert plastic bullet and shoot.
Great for indoor type target shooting. Had them for years!
I made up something similar using .45 Colt cases with modified prime pockets to use 409 shotgun primers and made my own wooden bullets the size and shape of a 250 gr. .45 bullet.
Bullets had 2 grooves cut for a pair of rubber O rings which would seal the bullet in case and seal along revolver bore.
They worked out really well for some in the garage target shooting into a back stop box.
Or you can use a brass case, primer only and use a hot glue gun and appropriate mold. http://castboolits.gunloads.com/showthread.php?17577-Casting-hot-glue-boolits
gramps
That style of box was on shelfs late 60s early 70s. Read the box and see what parent co winchester had at the time and where the ammo was made. Then check though web information may get you a more accurate date.