It will not fit without modification.
This can be fitted with a Dremel tool-grinder and power drill to the GSG 5P with modifications to both the inside of the brace cup and the pistol grip lower. (Best done by a gun smith unless you are comfortable doing the work yourself.) I did my own work and it turned out perfect. Note: Make sure you don’t remove to much material when grinding the inner cup or it will not fit firmly on your gun. The mod to the actual gun is simply drilling the pinhole in the plastic for the larger HK stock push pin. (You will need to buy the standard HK push pin separately.) • I really love this product and it will make your GSG 5 pistol one of your favorite guns to shoot!!! If done right, this will raise the value and functionality of your gun!!