I' ve used buckshot on a few deer. Never took more than one shot though. I always used federal 2-3/4" 00 in a mossberg 500 with a full choke. I' ve taken deer out to 50 yards with this setup.

Buckshot doesn' t give you as good of a bloodtrail as most other means do. I have no idea what could have happened with your deer, but I don' t think the buckshot itself was the problem.