Every training agency I've worked with over the last 10 years or so uses the Saf-T-Trainer plastic dummies.
http://www.brownells.com/.aspx/pid=9...SAF-T-TRAINERS
Having any kind of dummy round that can easily be confused with a loaded round is not a real smart idea. There might be "almost no possibility" of it getting mixed up at a bad time, but there is also "almost no possibility" of you needing your weapon or having an accidental discharge. There's a reason the word "ironic" is in the english language ....