Elite 2.0 Volt Mod. Pretty basic-brassed barrel, AR removal, tefloned plunger head, k26 spring, and custom catch spring. Not worth the effort. From my observations Elite 2.0 should be used as cheap
Nerf's Spring Arsenal Brings Modular Mayhem - GeekDad
Nerf N-Strike Elite Retaliator Spring Replacement - iFixit Repair Guide
Adventure Force Springfire Dart Blaster - Walmart.com