Guns and Ammo in Memohis TN had a Gen4 Glock 21 two days ago. They were out of the G21sf so all I could compare it with was a reguler G21. The grip was smaller and felt better in my hands. I have shot a G21sf, but it has been awhile. Working off of what I remember the 21sf to be, there was only a slight difference in the size of the grip.