This is my MBSMG (Masterdude Bullpup Sub Machine Gun). It has a new magazine I've developed for gray connectors which is more compact than earlier such magazines which I've used. It also has a new trigger which is created to make fast trigger pulling easier.

Pros:
-Good strength
-Good accuracy
-Semi-auto
-Removable magazine
-Newer, more compact magazine
-Bullpup
-Doesn't use too many pieces
-Can have optional front grip
-Rather easy to use
-Safety
-Trigger guard
-New improved trigger

Cons:
-Can be hard to load at first (But becomes easier with some practice)

More Instructables by me.

Note concerning images : Image one shows the MSAU with optional front grip. Image two shows version without it.

Step 1: Main Body: Components

Make the following. Letters are assigned to the parts for further reference:

Image 1: Make 1.(Part A)
Image 2: Make 1.(Part B)
Image 3: Make 2.(Part C)
Image 4: Make 3.(Part D)
Image 5: Make 3.(Part E)
Image 6: Make 4.(Part F)
Image 7: Make 3.(Part G)
Image 8: Make 1.(Part H)
Image 9: Make 1.(Part I)
Image 10: Make 1.(Part J)
Image 11: Make 2.(Part K)
Image 12: Make 1.(Part L)

Step 2: Main Body: Construction

Follow the images:

Image 1: Add blue and white rods to Part A and a small gear.
Image 2: Add Part B, blue and yellow rods, and a blue spacer.
Image 3: Add Parts C, D, E, F, G, red, gray, and 3-D blue connectors, and yellow and white rods.
Image 4: Add Parts D, E, F, G, H, I, orange, red, and gray connectors.
Image 5: Do as in Image 3, but no rods. Sorry but the image seems to constantly upload like this.
Image 6: Add Part F and a blue spacer.
Image 7: Cover with Part J.
Image 8: Add a small gear, Parts K and L, and silver spacers.
Image 9: Add gray connector.
Image 10: Add orange connectors, blue spacers, and metallic blue clip.
Image 11: Add 2 gray connectors as shown.
Image 12: And another one as shown.

Step 3: Magazine: Components

Make the following:

Image 1: Make 4.
Image 2: Make 1.
Image 3: Make 2.
Image 4: Make 1.
Image 5: Make 2.
Image 6: Make 2.

Step 4: Magazine: Construction

Follow the images:

Image 1: Add white rods as shown.
Image 2: Add the other parts as shown.
Image 3: And cover.
Image 4: Loaded with some ammo.

Step 5: Front Handle

Make it as it looks. No further instructions necessary.

Step 6: Use and Operation

To load remove the mag and place the pin in the appropriate area. Now place the ammo in the mag. Insert the mag into the ammo feed. Next push the white and blue rods in the ammo feed area out to the sides. Hook the rubber bands on the end of the barrel and the trigger spoke. Make sure the rubber bands are on both sides of the ammo. Once all the rubber bands are hooked push the blue and white rods back into the center. Remove the pin. Pull the trigger to fire (in case you didn't figure that out).

Image 1: Attach handle as shown.
Image 2: Insert magazine as shown.
Image 3: Ammo.
Image 4: Rubber band hooked on barrel.
Image 5: Loaded, view of midsection.
Image 6: Safety engaged.
Image 7: Safety disengaged.

Warning- This may cause harm or injury if misused. Do not point it at people. I am not responsible for damage, injury, or death caused by this instructable. Even with safety engaged it can fire. Always treated it as armed.