its ok , Madkill gave me the answer i wanted ...
for you skaterjoe , this Rail is for adding muchmore accessories ( im planning to convert my P90 in a savage hunter like the RWC's one )
see by yourself :
this is the nitro rail :
http://www.cobraairsoft.com/product_...07472245c5d452
this is the Savage Hunter :
http://www.arniesairsoft.co.uk/news/.../rwc-p90-l.jpg