Does anybody know if a ergo grip fit on the MP15-22 just like on an AR. I thought I read somewhere that I will need some sort of gap filler for the magpul MOE grip for it to fit on the Smith. is this the same for ergo grip

Fits fine. Have one on my 15-22 pistol.

No problem with the fit on mine either.

Same here, fits and works fine, there is a little gap between the rear tang and lower receiver. (Just like the Magpul MOE / MIAD grip)

Don't forget the two small springs when you pull the old grip off. AND check the spring depth (with a tooth pick) to make sure the depth is the same.