I modeled this after the Fortis SHIFT grip, but modified the unimportant parts (rear, cutout) to allow for printing without supports. 
 

Print Orientation

The model is oriented in the correct position (upright at an angle with the back face down). 

A stock printer should easily be able to print this with no supports. You may get a loose strand or two on the overhangs of the m-lok lugs, but i have been able to clip those off very easily.

Hardware

Both shorter and slightly longer Magpul m-lok screws fit through the center cutout, preventing the need for larger holes in the grip surface. Smaller holes are used instead to allow an Allen wrench through. 

Other generic m-lok hardware that I’ve tried also fits with no issues. 

Although the short screws worked best for my rail, you can edit the included step file to accommodate much longer screws. Simply extrude the recesses for the holes under the flat mating surface to cut all the way down through the curved grip area. This should allow you to install the screws from outside the cutout by inserting them all the way through.  Let me know if anyone has trouble with this and I can upload the modified variant.

Settings

• Material: PLA+
• Nozzle: .4mm
• Layer height: .12mm
• First layer height: .2mm
• Perimeters: 6
• Infill: 100% (may not be necessary, but why risk it)
• Hotend: 225°
• Bed: 60°
• Supports: None
• Fuzzy skin (optional): External perimeters 
  • Thickness: .1mm  
  • Point distance: .1mm