Gents,

Last night I was trying to fit a X300 onto my VP9, and it would not lock into place no matter how hard I pushed the light in.  Is the X300 compatible with the X300, or do I need different mounting system?

Thanks,

On the switch rocker panel that pivots so that you can install the batteries.  There is another small panel that is held in place in the middle by four small round silver pins.  Get a 1/16" punch and drift those in or push through so that the small panel can come out.  

Disregard the above.  I had to do that for the light to fit another gun.  I just looked at several of my VP9s and the ones with the X300 (170 lumen model) still has that panel in.  The X300U A (500 lumen) uses the same mounting system.  X300U B (600 lumen) is a different mount.  You just have to push the light on and it will lock in.  . Use the P mounting plate.  You can also loosen the side rails with the Allen wrench to tailor the squeeze tightness onto the rails.

I had to do the mod that DOE described above but now my x300U-A fits just fine on my VP9 with the pic adapter.

X300u fit just fine on mine.

The x-300 was tight going on mine, but finally fit with a push.

Remove the spacer.  Knock out four silver pins, top and bottom of toggle.

No issue on mine. Required a bit of push to click on place.