MDC,
There so many single trigger patents, with more info about the design, it's difficult to narrow it down...

If I had to guess, I would guess 77688 or 825550 by JJ Murphy

http://patimg2.uspto.gov/.piw?Docid=0082...View+first+page

http://patimg2.uspto.gov/.piw?Docid=0077...View+first+page

did it look like either of these?