I had to file a bit on the slide on mine as well. The slot was more like a figure 8 almost, with the center on each side protruding in a bit. Didn't take much at all to get it to fit. Biggest pain was getting the little bolt down in there, with a drop of blue loctite on it. Finally ended up using a pair of tweezers and spinning the slide around till the bolt started. Just snug, it doesn't need to be muscled tight, its not that big of a bolt. I have over 300 rounds through mine and it hasn't budged.