Handgathered and Machine rounded is the right response.
The sizes in these vary so much that it is only explained by a handgathering process
We are talking about the Toys R Us marbles here--- the 1" (give or take).
There was a special mail in offer to get two larger sizes around 2" and around 1--3/4". Vacor sizes are in "MM" (25mm for the little ones)and I am too lazy today to look them up.
These larger ones look much more refined ( I only have one of each) but Vacor was the one company that could pull it off at the time.
It seems to me that @stephenb ( respect!) was down in Mexico at the plant researching all sorts of marbles.
He may have received some wrong info here.
@Melissa has a nice collection of these--maybe she will step in with some wisdom from her collection.
Here are the three sizes that I own.
Marble--On!!