Amazon.com: NERF Modulus Recon MKIII Blaster, Removable Stock and Barrel Extension, Dart Shield, 12-Dart Clip, 12 Elite Darts, Outdoor Games and Toys for Boys and Girls (Amazon Exclusive) : Toys & Games
Amazon.com: Toy M4 Barrel Extension for Nerf Models with an Interchangeable Barrel Compatible (Black)
The barrel extension prevents it from firing, but it has to be non-firing for convention use anyway : r/Nerf