Today I bought an HW40 and was looking at some related info, found this guide to disassemble the HW40. It's in italian but the translation is pretty readable apart from, at one point it says to throw away the pin, just don't throw anything away, pretty obvious really. I apologise if it has been posted before.

http://airgunz.altervista.org/HW40PC...aggio_HW40.php