NERF HK MP5K barrel extention and guard

FAQ: **This model has a thin layer inside which supports the internal portion of the barrel which fits into your blaster. When you're done printing, cut the layer out using an Xacto knife or other tool.** I attempted to design all of my models so they can be printed without supports.

This is a NERF barrel extension modeled after the HK MP5K sub-machine gun. (At least it's supposed to be the K) You can read more about it on Wikipedia: https://en.wikipedia.org/wiki/Heckler_%26_Koch_MP5#M