I'm going to venture a guess, but if there is not a screw on the bottom of the grips you may have a set of hogue boot grips. You have to pull the grips downward. They origionally came with a little spacer that you inserted along the backstrap. If you take them off they are going to be near impossible to put back on without the spacer. You have to really pull hard on the grips while holding the cylinder area to get them off.