MEET THE TEAM: As a sense of scale, the blue Airsoft GBB is a USP Compact while the large one at the top is as long as my arm from stock to tip which I made to fire the really large rubber bands which I have atm. The red one is only 10 studs long and 3 studs wide (although the gears make it more like 5 studs wide which I'll do some instructions for. How to make a basic semi automatic rubber band shooter: Start by collecting single block wide pieces with holes for the friction pins/axles along the side, for this design you need at least two pairs of these preferably 6-8 studs long. Do the first part along one brick starting at the farthest most hole. The picture should be a good guide although I've done one whole side of the gun which means the trigger On the far right is the geat that you load the rubber bands onto. You can actually use any gear for this - in this case I used a small 24 tooth gear for compactness - although you might want to stay away from the wide ones that have come in recently. I suggest a 40 tooth one for your first build so you can see how it works. This is put in the middle of 3 block length axle and placed on the inside of the gun in one of the last holes. You then have an 8 tooth small gear in the middle of a 4 block long axle through the middle of the body so it meshes with the rubber band gear and then a 24 pin gear is placed over the outside end so the axle should stay in place with one block length of axle poking out. Finally you need another 5 block length axle with a one blcok wide spacer in the middle and a 8 pin gear on the outside so it meshes with the 24 pin gear in the previous step. There should be two blocks worth of width sticking out from the inside of the gun. To make the trigger you need to place another row of holed brick below the first which extends at least 3 holes further than the last gear on the first row. (Also, ignore the black gear on the floor, it should be in the gun at the end as in the first pic but it fell out and I didn't notice). The trigger is fairly simple as in it just needs to snap forward naturally (so there's some resistance as it's being pulled back) to a starting position but be restricted from going forward anymore past this point. As long as the axle is 3 holes along and one row below the last 8 pin as shown in the picture and that it sticks at least one bircks width outside of the gun you can pretty much do anything. My method is to take a 5 brick long axle with two half width L shaped pieces in the middle to act as the trigger and then on the outside to have a half length spacer and a half length 3 holes long plate with a small axle and another spacer on the other end of it for a small rubber band to go round them and then I place a stopper 2 holes away to stop the plate moving too far back and to act as a base for the rubber band to loop round. Once you've made your trigger, put some blocks with holes on the other side. You can now build the main body of the gun with a handle and a barrel. I find a 3 blcok wide friction pin through the end of a normal 1-block wide, non studded, holed technic piece makes the best barrel but anything that the rubber band wont slip on while it is on the gun will work. Your gun should now be a block with a gear at the back that should spin freely and rotate the internal gears, some extrnal gears that spin with the internal ones, a trigger and two axle-ends sticking out the other side (plus any other parts but we'll focus on these for the moment). You then need to put two half width 3-hole long plates on the rear axle and just move the rear gear (the one the bands will go on) which should make the axle with the plates on rotate quickly and the should spin round. If you have to exert a lot of force to make them move then try to loosen up the gun body and ensure all the gears rotate easily. The final piece is a bit esoteric; it's acually a 4 pinned gear. If you don't have one of these you find them in a lot of bionicle sets but a good substitute is two half width, 2 hole plates placed at right angles to each other (the acute angle facing downwards and towards the back of the gun). This needs to be placed on the front axle. Now test the mechanism by moving the band gear forwards and continue to apply pressure. The rotating plates should hit the 4 pin gear (or the top 2 hole plate) and slay there. Pulling the trigger should move the 4-pin gear clockwise and cause the rotating plates to 'fall' onto the next pin (or lower plate) - assuming you're still moving the rear gear forward - and releasing the trigger should release the spinning plates alowing them to rotate most of a revolution till they hit the top pin of the gear again. All that you need to do now is load a rubber band and fire. Simply take a rubber band and place one end between two pins on the last gear (i.e the band gear) and streach the other end over the barrel. If it doesn't stay there, try mounting the band further back on the gear. Don't worry if the band doesn't fire if you pull the trigger as long as the gear rotates (and only rotates a certian amount on each trigger pull). The gear should rotate 2-3 pins at a time so keep at least 2 gaps between each loaded rubber band, the reason for this is simply reliability, you'll get fewer problems with the rubber bands spaced apart Play around with the gun a bit and see if you can figure out how it works and how to make improvements to it. The best thing about lego guns is that you can easily modify them for example, see what I did to it afterwards: You should also try modifying the mechanism itself. The one I've shown you how to make is a variation of a very common one on youtube (like this one) with the Y pieces replaces by single pronged plates which just changes the gearing. My more succesfull design uses a Y-piece instead of a gear to load rubber bands onto which makes it much stronger and many, many times more reliable. It also uses a bullpup deisgn with the firing mechanism right in the stock with the trigger further forward. Mk over 9000 and an older version. So lets see your guns!