Well, here it is. My blue rod shooting, 7 shot semi-automatic k'nex gun.

It's no more or less powerfull then most sub-automatic guns, and is very reliable ( It sometimes misfires, but it never jams ).

It's not a perfect semi-auto, because you can't keep your finger on the trigger at all times. You pull the trigger and let it shoot back into place, and then pull the trigger again.

P.S. Sorry for the slightly blurry pictures, I don't have any good camera's.

Step 1: Trigger

This is the trigger. It should be easy enough to build.

Step 2: Left and Right Mech. Panels

1. This is the left panel, it includes all connections to the right panel.
2. This is the other side of the left panel. Make sure you put the 2 grey spacers on, they stop the back of the gun from collapsing inwards.
3. This is the right panel. It's basicly just the left panel without all the connection points.

Step 3: Firing Pin

This is the firing pin. You don't need to tape the spacers, but I did so because grey spacers tend to wear down. The trigger connects onto the ball joints.

Step 4: The Barrel

1. This is the barrel and magazine, what you will be building in this step.
2. First build this. There are 15 yellow connectors.
3. Now build the barrel. The grey connectors are decapitated. ( see picture 4 ) You can also break an orange connector in half.
4. You will need 2 of these, you can't use black ball joints!
5-6. Build the magazine.
7. Build the extra support
8-9. Attach these 3 parts together.
10. Add 2 metallic blue clips ( You can also use 2 spacers and 1 tan clip ) on each side.
11. Add the extra support

Step 5: The Handle

This step is pretty easy.

1. The side
2. The front
3. The back

Step 6: Put It All Together

In this step you will assemble the parts.
1. Add the trigger to the left panel. Make sure the white rod through the grey connectors goes through the hole in the white connector.
2. Now add the right panel.
3. Add the handle. Note that I turned it around, donÂ´t get confused.
4. Add the firing pin to the barrel.
5. Now add the barrel to the rest of the gun. YouÂ´re done! Be sure to check step 7 for the rubber bands.

Step 7: Rubber Bands

In this step you will add the rubber bands
1. These are the rubberbands I have on. you need 2 thick rubberbands and 6 small thin ones.
2. double up 2 rubber bands 2 times and put the on the trigger like so, one on each side.
3-4. Add the thick rubberbands and 3 thin rubberbands onto the firing pin and upto the front. Now test fire a few times. If you think it's too weak, try to add more rubberbands. But when it doesn't pull back the firing pin far enough, or not at all, remove some rubberbands. Try to get the perfect combination between pulling back distance and power.
5. Put the final rubberband on the magazine like so. You're done! load some blue rods into the magazine and fire away!.

Step 8: Grey Connector Barrel

This is a mod that will make it shoot grey connectors, which get you more range. Before you begin take of the entire barrel.
1. First edit the firing pin. Take the spacers of, and replace the middle yellow connector with a blue. Don't forget the green rod! This makes sure the red rod doesn't shoot of. Also don't forget the green rods on the yellow connectors.
2. Now remove the blue rod with the 2 spacers in between the panel, turn around the white rods, and place is as shown in the picture.
3-5. Now start the barrel. The pictures show the side, the top and the bottom.
6. Now add these rods to the barrel.
7. This is the magazine. You can see it is somewhat the same as Oodalumps'. It will hold 7 shots, if you want you can make it taller so it can hold more.
8. Simply add it to the barrel like this.
9-10. Add the firing pin to the barrel, and add it to the back of the gun.
11. Now just add some yellow connectors above the barrel, and be sure to connect them with a blue rod at the front.
12. And finally build the pusher rod.
13. This should be the finished product. Just add the rubberbands to the trigger, and to the front. Make sure you have at least one big, or a few small ones wrapped around the upper blue rods, or else the firing pin will be too low for the trigger to connect.

Now load it, add the pusher rod ( with a rubberband ), and have fun.