The upper is machined Aluminum the lower is polymer. Similar to the real SCAR. It is the closest replica to the real SCAR to date. You don't see many real Black SCAR's since the SCAR's delivered to SOCOM were all Flat Dark Earth color.
If you get a chance, stop by AEX and take a look first hand.
It's a 7.62mm sized mag. M16 use 5.56 sized mags. The H in SCAR-H Stands for Heavy thus refering to the heavier round and rifle build.. The real steel is built to throw a larger caliber round. Airsoft it's just to spend more money.