I found unluckydesigns' index grip to be very comfortable, but felt like the tolerance for the picatinny rail was too wide and led to the grip wiggling and twisting during use. Thanks to unluckydesigns for posting the step files, I was able to modify this grip in fusion360 to be a little bit tighter on the rail. I also made it shorter overall as on my blaster end of the grip was the longest part of the blaster.

I recommend printing this with 5 walls for durability, 10-20% cubic or similar infill. Enjoy!