The front slide rail on my FNX-40 has a distinct forward movement when pulling the trigger in DA. my FNX-45 does not have this issue. I have spoken to FN's customer service and they said an amount of movement on the front slide rail is completely normal. I have sent it back to them twice now and they have sent it back each time with the same slop on the front slide rails. Is this normal for the FNX-40?