Here are the instructions to the horizontal mag gun I posted a forum topic about. Enjoy!

Step 1: First Chunk

1) Make this (make sure you have all the blue rods and y-connectors on there.)
2) Make these 3 pieces
3-5) Add them to the first piece
6) Make this
7) Make these
8-9) Connect them
10) Add that piece to the first piece
11) Make these
12) Connect them
13) Add that to the first piece
14) Make these
15) Connect them
16) Add that to the first piece
17) Make these
18-19) Connect them
20) Add that to the first piece
21) Get this
22) Add it to the first piece with the other piece you made earlier

Step 2: Second Chunk

1) Make this
2) Add blue rod
3) Add green rod
4) Make this
5) Add to first layer
6) Make this
7) Add to other layers
8) Add these two white rods
9) Make this and put it aside
10) Make this, and make sure you have the green rod and the cut white rod.
11) Make these bits and pieces
12) Add that piece here
13) Add that piece there
14) And add the last piece there
15) Make this
16) Add it to the rest
17) Get this
18) Add it right here
19) Connect the two big pieces you just made
20) Add the trigger in, make sure you have the green rod there.
21) Connect the back part of that chunk to the bottom of the other chunk
22) Connect the front of the two chunks
23) This is very important! Make sure the y-connector is touching that blue rod but it should not be clipped in!
24) Get this piece
25) Put it in right here

Step 3: Finishing It Up

1) Make these
2) Put one here
3) And the other here
4) Make this
5) And attach it to the rest of the gun, this might be tricky so I recommend breaking the outer wall into different parts to make it easier to attach to the gun.
6) Get these
7) Add them here
8) Make these
9) Make the pin
10) Connect them like so
11) Attach the front of the pin guide here, you're gonna have to force it in a bit. It should go in the small hole closest to the back of the red connector
12) Connect the back of the pin guide like so.
13) Get these
14) Put the spacers on this rod
15) And add the green connector on top
16) Make the mag pusher
17) Put it in here

Step 4: Magazine and Rubber Bands

1) Make these
2) Connect these two parts
3) Add the last part
4) Make this
5) Add it here to finish off the mag
6) The mag goes into the gun like this
7) Put a rubber band here
8) Pin band, has to go under the guide rod.
9) Mag pusher band
10) Trigger band
11) Add this piece that I forgot about

All done! Go enjoy your gun. Load up the magazine with grey connectors with the open part facing the front of the gun and have fun!