Mounting X300 to Blue Gun Glock 17?

[walkingbush]

I own a small holster business and am trying to get an X300 to mount to a Glock 17 blue gun to use as a mold for a holster. However the rail slot on the blue gun and the key on the X300 don't match up. I'm using the Universal key currently. I've also tried my TLR-1 with the 1913 key in it and it doesn't fit either. I've also tried a Blackhawk G17 plastic gun with the same results. Is there something special I need to do to mount an X300 to Glocks or are the plastic guns just out of spec?

Thanks!

[PRGGodfather]

Tolerance stacking can occur with blue guns, too. Consider filing the U slot on the gun just enough to accommodate the TLR1's GL key, as it is the thickest of all weaponlights. Start on the slot side closest to the trigger guard, but both side may need relief. Compare with calipers on a real G17 and you should be GTG.