First, I removed the MOE standard grip that came with the rifle, but the MOE SL grip seems to possibly be out of spec where it is way too tight on the front surface where it fits on the receiver. Who knows, maybe they are supposed to be this way...
The corners of the receiver just digs into the polymer edges of the grip, I don't want to force it and damage the receiver. I just found a review of this grip on Midway where somebody said they had the same problem, had to shave down the inside of the grip and use a rubber mallet to install.