The M-80's I had as a kid all worked to my simple specs.
Some travel agent I used to employ called them the M-80, perhaps the term was interchangable? Yeah, the M-80 I had as a kid worked fine, right out of the box. Went to Mexico one time and found some M-240s and managed to get them over the border...they really worked fine, would actually nudge a buick from 25 feet!