Actually I found a great post on TOS from FALARAK 2 years ago.
http://www.ar15.com/lite/topic.html?b=3&f=16&t=271478
He tested and compared PRVI M193 against Q3131A. He even went so far as to pull and cross sectioned the bullets from both. Reader's Digest version...as to the differences in projectile, the shape of the boat-tail is different, and the opening at the base of the round is different, however jacket width is identical.
Bookmarks