This is the result of my attempt to make an "inexpensive" (uses few parts) semi-auto knex rbg. (rubberband gun) I got kind of tired of finding Knex rbg guns that are great but take a gazillion parts to make. In addition, it doesn't look too bad, either, being somewhat reminiscent of an M1A3 "Grease gun". You are welcome to offer ideas and/or constructive criticism. Please let me know how you like it. :D

Step 1: Photo of Parts Needed.

Honestly, I don't think I really need to list out all of the parts. A picture's worth a thousand words anyway. :P

Step 2: Making the Handle/ Grip

No description really needed, I think.

Step 3: Now, the Barrel...

Six "grey" spacers, (or 18 blue ones, six to a side) 3 to a rod, and four black y connectors. Note: The connectors (the y ones...) don't have to be y connectors, they can be just about any other connector you have on hand that'll fit... however, I find the y ones to be the best.

Step 4: Then, You Build...

This green and yellow bit, which gives structural support to the barrel, and keeps the end part of the barrel (the purple and blue piece, w/ the yellow piece and rod) from sliding towards the trigger due to the force of the rubber band on the barrel (end). Attach the blue and purple bit to the two grey rods of the barrel, and connect the two green and the one yellow rods to the purple connector already on the two grey rods. (hereafter referred to as the barrel).

Step 5: Attaching the Handle to the Barrel

Now, you're going to make the handgrip that goes on the barrel. Just follow the pictures.... BTW, the deconstruction of the barrel support is to make it easier to put the yellow connector piece on the barrel...

Step 6: Trigger Assembly

Okay, now we're going to make the trigger assembly and attach it to the gun. Basically just follow the pictures.... the two washers go on the blue rod, with the actual trigger in between. (You insert the blue rod in the white connector.... not any of the others). Then connect the other yellow connector to it, just as the other yellow connector already is on it. When finished, the trigger should "snap" into place when you rotate it into the yellow connectors... if not, then the little white rod placed perpendicular to the white connector might need a little adjusting. If it "still" won't click, then you might need to replace the white rod w/ another one. (Some of them don't seem to work quite right, for some reason).

Step 7: Assembly

Now, attach the trigger assemble to the barrel and grip. Next, add two blue rods to the pistol grip/ gun handle, and then you can attach the handle to the barrel of the gun. Now, if you "really" want to, you can go and start shooting right away, but there's still one more step before it's "completely" ready for action.

Step 8: Adding Trigger "spring"

Now we're going to add the trigger spring. I added this little bit because, in some of my earlier guns, if I used slightly stronger rubber bands, (I find the green ones that you get from Whole Foods to be fantastic) the gun would fire spontaneously. Well, this little bit stops that. Just follow the photos, "tying" the rubber band to the yellow connector on the trigger, and then looping the other end of the rubber band around (or over?..) the hand grip at the front of the gun. Congratulations! Now your semi-auto is all finished and ready to go!

One note: In case you don't know how to load RBGs, (Those that "actually" fire rubberbands, unlike some...) what you do is you loop the rubberband around the orange connector at the end, so that a section of the rubber band is inside the piece, as it were, (in between the two edges of the connector, where you normally would connect a rod) and then loop the other end of the rubberband around the little green rod on top of the trigger.

After you've reloaded, just aim, and pull the trigger to fire. Before you click the trigger back in place, there's a note about reloading below:

Another note: The reason the trigger is designed that way is simple: faster reloads. If, after you've fired, (pressing your finger against the "other" green rod on the trigger) you reach around with another of your fingers and press down on the yellow connector (that just came away from the barrel) about as far as you can, and then let go of it completely, it'll snap back and "click" the trigger back in place. :D

One final note: (I promise!) If anyone knows what size those green Whole Foods rubberbands are, please let me know. Thanks a bunch!