We get more details on the newly released MadBull Airsoft Metal M4 bodies which come with 8 markings that you can choose from. These are all licenced markings,  and CNC'd deep engraving and the body is made of T6 aluminum material. The metal bodies are compatible with most TM-based receivers from other manufacturers and of course MadBull Airsoft accessories:

"8 LICENSED M4/ AR models: Stag Arms, Noveske, Daniel Defense, Barrett, PWS, Gemtech and Double Star

Features:

• 3D design from scratch (not just copy others)
• T6 Aluminum material
• Authentic trademark
• Deep "CNC" trademark engraving (Not cheap laser engraving)
• One world-famous MadBull Ultimate Hopup ($40 USD value) with optional LED tracer function
• Matte silver steel color pins (decorative)
• Compatible with most TM, JG, CA, and Echo1 AR/ M4. (Small modification may needed)
• Compatible with all MadBull accessories, including Handguard rails, Outter barrels, Hopup systems, Inner barrels, and receivers.

MSRP: $99 USD

Manual: http://www.madbullairsoft.com/doc/Manual/M4%20metal%20frame%20User%20Manual-2.pdf

Review: First impression review by Arnies: http://arniesairsoft.co.uk/news2/9635