Capping grades is a horrible idea. Imagine taking a course and realizing there was a limit to who could be successful. This will destroy motivation.
A better solution is having a more transparent and objective process for measuring student performance. This is literally what I’ve been working on. If after that, too many students are achieving A’s then maybe you could make the course more cognitively demanding, but that means that your course activities need to match your course claims and objectives. Which would mean making the course objective more ambitious.
Breaking news: Harvard faculty votes to cap the number of A's awarded in course grades, a big step in combatting the grade inflation that has been dumbing down our courses, conveying the wrong message to students, and making universities a national laughingstock.