This is my first project that implies mechanical parts, but in the end all worked well.

The Ballistic Knife is a Special secondary weapon that appears in Call of Duty: Black Ops, Call of Duty: Black Ops II, Call of Duty: Black Ops: Declassified, Call of Duty Online and Call of Duty: Black Ops III.

The Ballistic Knife is a secondary weapon. It is a one-hit kill when fired as well as when used to melee. 

A ballistic knife is a knife with a detachable blade that can be ejected to a distance of several yards by pressing a trigger or operating a lever or switch on the handle. Spring-powered ballistic knives briefly gained notoriety in the United States in the mid-1980s after commercial examples were marketed and sold in the United States and other Western countries.

This model is divided in several pieces to be easily printed. To make the model work you will need 3 springs, 2 compression springs and 1 torsion spring. The blade is divided in 2 pieces in order to be able to printed flat on the printer. The case, where the bigger compression spring goes, is also diveded in 2 pieces and the orientation is important at the time of printing it. 

The other two pieces are easy to print.

I decided to make this desing as a challenge using mechanical parts and because i spend a lot of hous playing to call of duty and using this weapon.

Steps to build it:

1. Print all the files. The blade needs to be printed 2 times.

2. Found the springs, the compresion and the torsion springs have to be small, you will see more a less the size when you print the files. In my case i used a spring from a pen for the button.

3. Before gluing the pieces of the case of the blade, i woul recomend you to put the trigger, attaching it using a piece of filament, a road of tin or similar and going through the contorsion spring. Once this is attach you can put the button with the smaller spring. Now that all this is in place you glue the other part of the blade case.

4. Finally introduce the bigger spring in the blade case and after that the blade. Where you hear a little click or you see it your weapon is load, so be careful where you pointe it. 

5. If you want you can make a security pin using a tin or similar material.