I experienced the same problem with my Kimber.
I noticed that if the magazine was inserted with the slide open, the bullets would feed most of the time. If the magazine was inserted with the slide closed, the bullets would jam into the bottom of the feed ramp while attempting to rack the slide. The problem was not with the gun, it was the magazine. There was not enough force in the magazine spring to push the bullets up to the right angle. I switched to another magazine and it worked fine.
I took the spring out of the defective magazine, stretched it a bit, then reinserted it into the magazine. Tested it in the gun and the problem was solved.