As mentioned above, the differing designs of the internal actuating lever on the HW40 and Beeman P17 (or at least, my P17).

http://i301.photobucket.com/albums/n...man10-Copy.jpg

HW40 (on the left) uses a thin steel plate, with a fancy wire spring sitting around it.

P17 has a thicker alloy casting with a coil spring set in it.

http://i301.photobucket.com/albums/n...man11-Copy.jpg

How the P17 lever works, fitting it outside the gun. As soon as the gun is opened, and the compression cylinder rises, the lever is able to rock back - forced by the spring, that is - and the right hand tip of it pushes the safety 'on'.

Bear in mind, of course, that the external button/slider of the safety catch extends further forward than it does inside the gun.

Iain