Dissasembled my nerf stampede while currently in a paint and build mod for my longshot. I learned how to remove the air restrictor, thus allowing for more power. Although it is considered complex for being fully automatic, the design is quite simple and typical for most nerf guns.
I will be adding a complete disassembly instructable when I paint mine. Since this is an electric gun, the internals that involve movement should not be painted. Period. Paint them if you want, but it's your funeral.
Step 1: Dissassemble
Now, the first step is the hardest (sarcasm). All you have to do is remove the battery compartment. Simple.
Step 2: Dissassemble (2)
Now take out all the screws on the exterior of the gun, including the ones on the orange. The orange front is actually screwed onto the yellow body from the inside. Now caution should be exercised here. The firing switch connects through the handle, so it is best to fold down to not damage the electronics. Also, at the top is where the cylinder is located. This is where we will focus. Remove the protective "plating" over the cylinder and the release mechanism. In front of the cylinder is a two-piece bracket holding the black spring in place. Now you are able to remove the cylinder from the gun.
Step 3: Cylinder Dissasseble and AR Removal
Now that we've removed the cylinder, we can take that apart. Carefully remove the black spring (just so that you do not stretch it or something). On the back is two screws. Take those out. Removing the back, we are able to gain access to the plunger and spring. Remove those. (Note: this is also benificial for a spring addition/mod. Doing so will increase the amount of power.) Also remove the white rail, as this slides easily without the back attached and will only get in the way. REMEMBER WHICH WAY THIS FACES!!!!! It is an important part of the mechanics and accidentally installing it backwards would only cause your gun to malfunction. Now we are left with an empty cylinder. The large and initial air restrictor can be accessed from the back with a long drill bit. If you are crafty (or just risky), you can remove the black part, for that contains the small air restrictor. This can also be removed with a small drill bit from the front. AR removal is really just a personal preference of removal, and any beginners can learn from other places on the internet (but hopefully if you are reading this you are know at least what you are doing). NOTE: if you drill through the entire piece without dissassembling the black piece, you will encounter a spring. For safety reasons use caution. Don't want you to hurt yourself.
Step 4: Reassembly
Honestly, all you have to do is completely reverse taking the thing back together, and viola! More power! Happy Nerfing!