Latest product from Hadron Airsoft Designs, is the clamp on upper RIS.
This device uses the existing upper rear sight to secure itself. No screws needed.
Simply drop over the rear sight, front first. Then, gently prise the rear of the mount open. The sight will pop onto the existing mounting.
Fits in seconds.
Please note, if you are going to use heavy scopes, or treat the pistol in a rough fashion, then we advise that you bond the mount to the pistol upper. Either glue, or ideally SUGRU material, which is non damaging.
Please take your time fitting this device, do not try and force it in place.