Building a knife

[mazhar]

THE KNIFE NAME IS BALLISTIC KNIFE and it was invented by Russian special forces or the Spetsnaz
just GOOGLE IT under the name of ballistic knife and you will find it
and the spring is steel with a thickness 3 mm and the measurements of the spring depend totally on the length of the handle or the housing i mean because the spring length must be double the length of the housing and that will make it hard to cock but it will be fast and accurate