My police service weapon is the .40 cal XD Tactial model. When the last round in the magazine is fired and the mag is empty, the slide should stay locked to the rear. This past time at range it never locked back a single time. Its not the mags, I tried all three of my mine and several from other patrolman. The springs were "exercised" and tried again. Still had the same problem. It shouldn't have been the rounds I was shooting. We were all shooting the same rounds, but I was the only one experiencing problems. I wasn't "limp wristing", the weapon was cycling fine. I have shot this weapon for 2 years including hundreds of rounds while in the police academy. Any suggestions would be appreciated.