Sounds like you may have a burr on the mag release, or the release is out of spec.

It's simple to remove. Make sure the weapon is empty.

You'll need a small flat headed screw driver that will fit the screw on the right hand side of the catch.

Depress the Mag catch and then insert the screw driver and turn the screw untill it stops (about 90degrees) now remove the catch from left to right.

This is a MIM part {simular to cast} and may have a crease from the mold that needs to be stoned down a bit. OR you could replace it with a better quality part like one from Ed Brown Ed Brown

Quoted: Could also be a grip screw bushing protruding into the magwell.

My first thought also, except the part where he says "if I depress it about half way, the mag will drop free.

Quoted:  Just for the record, this Kimber uses an allen screw to retain the catch, but Kimber is nice enough to supply a wrench with the weapon.

Cool...........