This is my first part, so if there are corrections you wish to make feel free to change anything to make this better.

I could not find a good Glock 44 sight solution so I planned on purchasing a new slide with slot for a Sig Sauer Romeo Zero. Unfortunately, that slide is back ordered. I created this in Tinkercad and after a bunch of trial and error I got this. It fits snug in the rear sight slot, just slide the rear sight out and slide this in with some force. I used 2 M3X12MM flat countersunk screws with a washer on the red dot body. I am waiting for my 10MM to come in to see if its a better fit. 

After firing 200 rounds with no misfeeds or jams I think this works great. I printed in ABS and PA6-CF with a .6 Nozzle on a P1S. Both fit, but it takes some work to get the screws into the holes. When I removed the ABS one, the holes do not hold as snug, so I just printed another one.

Again, I am a newbie with this stuff and have only designed a few items in Tinkercad. If you are a Freecad SME and would like to use this model to improve, feel fee to do so. 

Print Settings 

Material: PA6-CF or ABS

Infill: 50% 

I used a .6 Nozzle