Well you're probably right.  You may need to stick with the darts.  How much volume does one of those guns hold?  What if you have to shoot the animal a second time?  Wont they run away?  Acctually roping cattle is not stressfull on them if they are handled correctly.  I ride through my cattle every week so they are use to a horse and that makes it so much easier to handle them when necessary.  I know some farmers in the area that hire cowboys to check their cattle for that reason.  It saves so much time and labor when the cattle do need attention.  That's the cowboy in me.  I'm sure some farmers would feel differently.