It seems to me you get a higher pitch with more lip pressure, and a lower pitch with light pressure. It's funny, because my concern is to get a very high pitch. Sometimes I think my Power bugle is too low! I'd say that 95% of the bulls I bugle with are higher-pitched than my Powerbugle.

The chuckle takes more practice for me, and to further complicate matters, the chuckle seems too high-pitched to my ear. I do most of my chuckling with my throat. It's really not a tough sound to make that way. I'll bugle then pull the bugle out and throat-chuckle.

You can get a real gnarly growl out of the bugle by starting with a normal call, then twisting the call in your mouth so one edge starts to come away from your lip.