K'nex Semi-Auto Belt-Fed Rifle




About: I do K'nex...a lot. It's fun to mess around with new mechanisms, and to learn about basic engineering. I build mostly guns, and love to build new concepts. I will start posting some of my 'unposted ideas' in...

(Please read everything)

Well, after two weeks of hard work and failures...here is my Semi-Auto K'nex gun. This system of Semi-Auto has never been used before, as most semi-auto's on this site are hammer action. This version of semi-auto runs on an internal slide, and a sliding trigger. In step one, you can see how the mechanism works, and I will be posting a video. It has not that great of a range, but it's better than most, and is reliable.

This originally was meant to be my Belt Fed Rifle with Oodalump's K'nex W.A.S.P blended into it, but I am not a big fan of copying people's work, even if I do give them credit. So, I made my own Semi-Auto system. I will take credit for this, and if anyone wants to use it, feel free. But please credit me for the system.

Also, this gun is not yet finished. I will be coming out with a V2 in a week or so, and if you build it and mod it, I might include some mods you made into it.

Also, I am including pictures of my original drafts and designs, so you can get the feel of how I work through a gun, and maybe even help you guys with planning and creating your own semi-auto. Some of these ideas could be edited by you guys, or whatever you want. You don't have to look at them, but I thought it would be cool to show you guys.


Stat's/Pro's and Con's





Belt Fed

Holds 15 rounds+

2 in. pullback (kinda good for semi-auto)

In my opinion, this gun looks amazing. Kind of futuristic.


Not-so-great range 15-20 ft.

Trigger has a lot of pressure on it. If you don't reinforce it with tape, it will break eventually.

LONG trigger pull. I don't really like it, but it's the only way right now. Your hands will have to stretch a bit.

9 cut pieces....8 of them are required :( sorry


Well, That's about it for the gun. I hope you guys like it, and feel free to mod this to your liking. If you build it/mod it, please post your progress in the comments and I'll add them into this instructable.


Unfortunately, I'm only going to post instructions for the mech.... I don;t want to spend a lot of time on the rest, because it's actually a confusing front end of the gun, and it'd be hard to explain with pictures. Feel free to make this a turret gun, a mag-fed gun, or a different version of a belt-fed. Overall, just have fun with it. Also feel free to mod up the mechanism, and see it you can create a system with less cut pieces, or even better, no cut pieces.


One last thing, I don't know what to build next, so it would greatly appreciate me if someone gave me some ideas and suggestions. I'm thinking about a full-auto mechanism, but I'm not getting very far right now. It's pretty challenging.


Please leave your thoughts in the comment section. Please,please, please. I really want feedback on this gun, just because it's such a cool concept, (in my opinion). This is one gun that I really want your criticism on too, haha, I just want to know what would make it better.

Step 1: Mechanism

Well, this is the mechanism of the gun and the original drafts that I wrote up. The trigger has a little extension that pushes that ram back, and can only turn one way. The trigger runs on a slide, and has a rubber band to reset it.

The ram has a 'block' that the trigger pushes back on. When this block reaches a hole in the 'roof' of the gun, it pushes up and has room to shoot back into original position. When the trigger comes back to reset, the 'extension' rotates, then is re-rotated as it passes the ram's 'block'. That may be hard to understand, but the pictures show a pretty good understanding of the mech. If you have any questions, feel free to ask away.


And here's a couple video's -




I'll be posting a full review of this gun this week. If anyone else wants to review the mechanism, feel free, I would appreciate it.

Step 2: Mechanism Instructions

Follow the pictures and mod it to your liking. Hope you like it!



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    21 Discussions


    3 years ago on Introduction

    I like the gun, honestly it could look better, but I have a feeling the effort went into the mech.

    Also I was wondering if you had a belt that loaded itself, or if you had to put it inplace. I know I made one which I never posted, and it was always really awkward to load.


    GREAT JOB!!!!!!!!!!!

    1 reply

    Reply 3 years ago on Introduction

    Thanks! This gun works like a turret, so a rubber-band pulls the next 'belt piece' into place after one is shot. So, the only time you'll have to reload is when the belt is empty. Thanks once again!

    Lucas The Boss

    4 years ago

    They have change the site around so I don't know how to send a private message anymore but dident I tell you about a pump I was working on, we'll once I post my crossbow I was wondering if you could help because I am having a ton of problems with it

    3 replies

    Yeah sure! I don't have skype or anything, but if you sent some pics to my email, (lincolnschroeder123@gmail.com), I'm sure I could help out. Or you could post them on my orange-board if you'd like. And to send a private message, go to my page, ad next to my profile pic, it has a button that says 'Send Private Message'. Hopefully I can help out with your pump!


    4 years ago

    Wow this is really cool can't wait for internals!

    PS why didn't you upload it to youtube instead.

    1 reply

    Reply 4 years ago on Introduction

    I don't have a youtube account...and wevideo is the only program where I can make videos with my laptop :/...Thanks though!


    4 years ago on Introduction

    This is hella nice. I would like to see internals see what I can learn from it and make my own. Also I might incorporate it into my prototype machine gun. And I love it, keep up the good work. I'm going to subscribe, oh wait, I did that all ready lol. :p

    1 reply

    Reply 4 years ago on Introduction

    Haha yeah I forgot to thank you for subscribing, so thanks! I'm actually working on the instructions right now, so it won't be long. Thanks for the feedback!

    Yeah...when I post my original belt fed gun, (non-semi-auto), you can see that this belt fed was meant to be a belt fed that didn't have to have a bunch of block triggers. It runs just like a turret.