Early season, I do it every year. A couple five point sheds on my Kifaru weigh nothing. When things are really quiet, midday, get in high on the mountain and start a calling sequence. Some quiet cow calls for 10 or 15minutes.. Nothing responds, move into some location bugles and the challenging. Ramping up till pure bugling back and forth at yourself. Then, take a break for a few minutes to pique interest... Start to tickle the antlers, then an all out war, slamming them together, make sure to grunt and moan. Any breaks you take have a bugle in them. You gotta make a good deal of racket, for five minutes or so at least. Every year I have quiet hot early middays turn into loud ones while doing this. When the other bulls join in, it's nice to have a partner sitting a ways off so he can hear. When they do, I usually keep at it as long as I'm comfortable. But there's a lot to be said for letting those bulls that are finally worked up come like a bird dog and search.
Be aware that Bulls that come vocally to rattling often stop and rake trees before getting too close. That's you or your partners chance to move in. Good luck!