Yes, the Dragun series will work fine on CO2. As to your question about the reg/expansion chamber: it depends on the Dragun you buy. The original BD (the one that doesn't have the LCD screen) does have a regulator (a pretty crappy one according to most BD owners and you do have a foregrip to grab. On the newer E2 however, there is no regulator, but there is a gas-thru foregrip. This will essentially act as an expansion chamber.
So, yes the entire BD series has foregrips.
'05 Proto Matrix
Techna Finger Job Style Trigger, CP Dust Black 12" Pro Barrel, CP Dust Black Twist Lock Feedneck, STD Industries Proto LPR, Orange SAM Proto bolt with Tophat Mod, Proto Low Pressure Bolt Rear Cap, Tadao M3 software, Hybrid Red Lady Grips, Black CP Black Razor Drop, Pure Energy 72ci 4500psi HP Peanut tank, Red Halo B with V35