Semi Automatic Knex Gun




This is a semi automatic gun that uses cartridges which can be loaded from the top. After one cartridge is fired it falls out the bottom and the next one falls into the chamber. The gun is gravity fed so it can only fire as fast as the cartridges can fall, but it will shoot almost as fast as you can pull the trigger . This gun shoots hard so if you build it be careful.

Step 1: The Chamber

The chamber is essintially a set of rails which the cartridges will slide down and a firing bar which will hold them until they are fired.

Step 2: Trigger

The trigger, when pulled, will break the orange part off the cartridge and release the bullet.

Step 3: Trigger Handle

The construction of the handle.

Step 4: Deflector

The deflector will keep the orange piece from shooting to the ceiling after it breaks off.

Step 5: Barrel

The barrel is for looks and so you can hold the gun, it has no effect on the bullet what so ever.

Step 6: Handle

Just a hand hold.

Step 7: Magazine

After this is installed the gun will be able to hold five shots.

Step 8: Cartridge

You will need to have these orange pieces which come from the old roller coaster set. If you don't have them you will need to just add the little blue spacers to keep the white end from sliding. The gun will be able to hold five of the cartridges. Once you have built a cartridge you may want to slide it through the gun before you load it to make sure it falls freely. It should fall all the way through the gun without you pushing on it.

Step 9: Loading and Firing

You load the cartridges like in the picture. Hook the bullet through the rubber band, pull it back through the hole in the white end and attach the orange piece to it. Once you have it loaded, drop it into the rails at the top and let it slide down to the firing bar. When you pull the trigger, the orange piece will break off, releasing the bullet and letting the empty cartridge fall out of the bottom of the gun.



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    14 Discussions


    8 years ago on Introduction

    I like your idea. Though, I tried to make a sniper where the orange connecter held the bullet back sort of like yours and the rod slipped right out of the connector after a certain tension. Good idea though.

    2 replies

    Reply 8 years ago on Introduction

    Lol It actually slipped out earlier than expected but yeah it still had a lot of tension on it. Would have shot really well though :P.

    agent harmsy

    9 years ago on Introduction

    I agree with Oblivitus, it could use a LOT of refining, but new mechs always do :P


    9 years ago on Introduction

    Nice design, I hope that others will continue to improve this.


    9 years ago on Introduction

    I have seen this done better on youtube. You could probably try to build up the frame to make it a bit sturdier and a little less clunky. You also might want to make the cartridges a bit more compact in order to increase magazine capacity.
    2 replies

    Reply 9 years ago on Introduction

    I could have, two or three years ago when I found it. Now it'd be nearly impossible, what with not knowing the name or having the time to sift through the thousands of knex videos. I'll give a link if I happen to find it.