Note: This will not tell you how to make the whole gun. This only tells how to make a new mag so you can fire new ammo. If you haven't made the MAR yet then here is a link.
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Step 1: Making the Components
Picture 1: Make 2.
Picture 2: Make 1.
Picture 3: Make 1.
Picture 4: Make 1.
Picture 5: Make 1.
Picture 6: Make 1.
Picture 7: Make 1.
Picture 8: Make 1.
Step 2: Construction
Picture 1: Add white and blue rods where indicated.
Picture 2: Place the earlier made components as shown in the image.
Picture 3: Place the earlier made component as shown.
Picture 4: Place white rods where indicated on the earlier made part.
Picture 5: Place the other already made part as shown.
Picture 6: Add light gray connectors where shown.
Picture 7: Place white rods with tan connectors where shown.
Picture 8: Place the earlier made part as shown in the image.
Picture 9: Connect the components you made as shown.
Picture 10: Add the last part you earlier made as shown in the image.
Step 3: Putting Everything Together and Firing
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.