I'm really stumped by this. What should be the easiest part of assembling a stripped lower is holding me up.

I have a spikes tactical SL15 lower with a Daniel Defense lower parts kit. Everything is done except screwing in the pistol grip. I put in the selector detent, spring, and the pistol grip and screwed it in. When it is all the way screwed in its about half an inch shy of being tight to the grip, and therefor has all kinds of play.

What in the world, my only idea is to buy a shorter screw. Anyone have a similar experience or have insight why this part wouldn't work.