We have a team that has recently done a lot of experimenting with rubber bands. After interviewing a rubber band engineer (yes, there really is such a thing) what was discovered is placement is key. You want there to be almost no pull on the rubber band before pulling back. You also are better off with a shorter stroke and more rubber bands than a longer stroke and fewer rubber bands if consistency is the goal.
The longer you stretch the rubber band in distance, the longer you stretch it in duration, and the more times you stretch it, the less consistent it will be over time.
Our team that is using a linear puncher was needing to change rubber bands in practice after the equivalent of after each match. After making changes on the robot, they did not change them at all at a tournament where he had 10 matches plus practice, skills, and eliminations and the puncher was rubber bands were consistent all day.