I hooked up three 9.6V batteries to my nerf vulcan. Now I need to mod the battery compartment to hold them and build some longer chains. It goes through 25 rounds in about 3 seconds.
This was inspired by ManaPotion's 500 RPM Vulcan mod. I've reached their fire rate, but hope to push it a little farther with some heat sinks and better motor cooling. One more 9.6V battery should push it to 666 rounds per minute.