Here is how to mount Leupold Deltapoint Pro on FNX 45 Tactical. I have researched the internet for hours and have also contacted FN customer support, but I found nothing that solved the problem until I came across this.
Step 1. Install Leupold Optic Plate 171203
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The best way to install the mounting plate using the screws provided in the package.
- Tighten to 18-20 in-lbs to the slide

Step 2. Secure The Leupold DeltaPoint Pro
Install DPP and tighten the M4 X 14mm torx head screws to 18 - 25 in-lbs
Check torque for every 1000 rds
The only down side is that the plate doesn't lock against the slide, and it's hold by screw tension. So torque check is important.
There is also no iron sight co witness.
Other Options
Filing off the front part of the optic body helps to fit the optic without having to do anything to the rear sight.
The DeltaPoint Pro footprint fits the slide cut cover plate holes, but the optic is slightly longer so it doesn't line up.
If you would like to return to a RMR optic, please check out our FNX 45 Red Dot Sight guide for more information.
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