spikes tactical (or fail zero) nickel boron BCG
this is quite the interesting piece. i picked one up a few weeks ago. i have yet to shoot with it due to school and weather but ill give you my preliminary report.
the thing is SLIPPERY. i mean you hold the thing in your hand and half expect it to fly out. when loaded in the receiver, it glides with zero lubrication. you don't even hear a thing but the buffer spring. they say it never needs to lube and i believe them, although most use a tiny bit anyway just in case. people have said carbon wipes right off with a dry cloth and again i believe it. ive tried rubbing some dirt and various substances on it and seeing what sticks and what wipes right off and so far nothing has stuck.
they come in at $200. if you are looking at a plain old phosphate bcg for $120 and on a budget, this probably isn't worth it. its super cool, easy to use, and probably lasts longer, but its not a must have. however if you are looking at buying a chrome one for $180, its definitely worth the extra $20. as with everything else i review, ill try to update it when school slows down and i have time to shoot. ill get pics soon too.