Ehhh...I'd be a little nervous. Here's an AR (556) which broke a fortis rail:
Thread: http://www.m4carbine.net/showthread.php?135012-I-blew-up-my-rail
Have you thought about putting a Noveske Pig on there instead? Honestly, on a 9mm, that may be more useful anyways....
I would never do that with a 5.56. I just thought with a 9mm, I wouldn't have many issues. I don't want to pay for a noveske pig, as this is temporary until my suppressor is approved.