We recently got our hands on a Kimber Sapphire Ultra II and took it out to the range to run some practice rounds through it. We found that the firearm didn’t like FMJ practice rounds, but had no problem with self defense rounds.
We then compared the rounds’ overall lengths as well as profiles to see what the differences were. We did not have time to chrono the rounds to see if powder charge had anything to do with it, but we plan to as the Sapphire has a 16 lb recoil spring in it which could make a lighter load round not allow the weapon to cycle properly.
We came to the conclusion that while overall length and shape of the tip of the rounds may not be the only reason for the misfeeds, it clearly was a contributing factor. Check out the video below: