I traded in my G27 years ago, but I used the Pearce extensions....from what I remember, it didn't quite fit the extra round very well....its been a long time though. I thought they were worth it just for the extra grip surface. Even with that though, I hated my 27, especially because of that empty space in the palm of the hand. The grip extension let's you wrap a finger around the front, however it doesn't extend the grip surface in the back, leaving an empty air pocket in your grip.