Just updated this listing as I had some question about Gen4 compatibility. These were all bought new last year, and it looks like they have the two grooves, but I'm not sure if one of the grooves was made by the factory, or manufacture. Like I said, none of these have been used, and if there is any problem whatsoever I'll be happy to refund. I'm a long time seller on Ebay with great feedback, but as you all know, they don't allow the sale of extended mag. Also I won't ship to States where these are banned.