If you're using reloads for 9mm carbine, pay attention to the reloading manual. Some of the loads I've found listed have a note (*not for use in rifles").
I started out with 147 grain bullets and found that the timer had trouble picking up the sound of the shots. I switched to 124 grain and haven't had any more problems.
I don't think he's worried about a timer at uspsa or steel challenge, just some fun pinker loads.