For those who do not know, a ballistic knife is a knife that gets expelled from a barrel. Similar to how a bullet is expelled from a gun barrel, except instead of an explosive force driving the knife, a high power spring forces the knife out. BEFORE CONTINUING!! this is very dangerous! In one of my pictures below, i actually use a drumstick instead of a knife because I would not like a knife sneaking up into my chin.. That being said, this Instructable id for educational purposes ONLY! I will not take responsibility for what you do with this information.. Lets GO!!

Step 1: You Will Need...

One crutch (like when you have a broken leg) i used my sisters so it was free but you can get one a t salvation army for like 10 or less.

high powered spring-mine was 3.50 from http://www.mcmaster.com. Make sure that the spring is slightly smaller than the crutch so that it can go inside, but you still get maximum power.

Knife (or drumstick if you want to play it safe).. i got mine from china town for 10.

NOTE- in the picture im using a wimpy spring from an old airsoft gun.. didnt get too much distance but the spring i ordered from the link above works beautifully.

Step 2: Get Into the "barrel"

Your going to need to press the silver nubs to take out the head of the crutch.

Next, insert the spring into the "chamber"

Now take off the rubber tip.

Step 3: Put the Knife Where the Rubber Tip Used to Be

If the knife is too big, it wont fit. Period.

BUUUT! if its too small, you can clamp the metal with a vice grip and fill in some space with hot glue.
Here I am using a drumstick just for demonstration purposes.

Step 4: Aim and Shoot!

With larger crutches, your going to want to hold it almost like a sniper rifle.
Or you can hold it from the hip (ex-how Al Picino, hel phis gun at the ed of Scarface, when he blew up the door)

This is my first published instructable so please be nice haha. Constructive help is always welcome