Airsoft Atlanta reviews the Tipmmann M4 HPA/CO2 Airsoft Rifle and this is now available at their online store... "The Tippmann M4 Carbine is a full-auto CO2 or HPA gas airsoft rifle.  Includes Tippmann’s awesome warranty. Key features include the Tippmann proven inline bolt system, adaptable air system, rate of fire and velocity adjustability.

The M4 Airsoft Carbine features a realistic flip-top break down design like a true M4/AR. Its versatile air system uses either a 12g CO2 cartridge in the 80 round magazine, or the built-in remote line for attaching to a HPA external tank. It’s also compatible with standard M4 hicap or midcap magazines from other manufacturers like JG, Marui, etc (30 to 300 rounds) when using the HPA setup.  If using the CO2, you must use the Tippmann magazines.  The M4 Carbine has a metal receiver and is compatible with many actual M4/AR components including a rear stock, front shroud, and standard Picatinny Rail System.

NOTE: This gun is designed to take 800 PSI input pressure. SLP tanks and air rigs are not recommended.

Features:

• Multiple Gas Input – CO2 Cartridges or Remote Line Adapter with HPA tank
• Gas Blow Back - Realistic Recoil/Kick
• Full Metal (Aluminum) Receiver, Barrel Assembly and Stock Tube – Breaks Down Like Real M4
• Adjustable rate of fire – 8-15- RPS
• Adjustable velocity – 300-400 fps (0.20 g BB)
• Adjustable Hop-up Bucking
• No Batteries
• Firing Modes: Safe/Semi/Full-Auto
• Adjustable Front and Rear Flip Up Sights
• Front and Rear Sling Mounts
• Anti-Jam Technology
• Low Maintenance – No Gear Box
• Easy Disassembly
• Tool Less Mag Disassembly
• Full Length Top Pic Rail
• Modular Foregrip – 8 sided picatinny capable With Additional Rails included
• Glass Filled Nylon grip
• Optics Ready with Flip Up Sights
• Adjustable 5 Position Stock
• Accepts many real AR stocks and handguards
• Works with many AEG mags when remote line system is used
• Remote line adapter included
• Accepts industry standard AEG inner barrel
• Threaded Flash Suppressor (M14x1.0 CCW)"