[Azathoth]

Their is a thread somewhere on ASC where people review metal bodies. I have a post on their about a G&P or a Magpul PTS body and have picture of it broken. That said i've seen plastic bodies crack and break as well.

If you want realistic weight, get a pot metal body and a pot metal barrel. A real weighing gun out of the box is a PTW. Stainless steel barrels on real firearms make them much more heavy than 'modern' (2012+) airsoft guns. Their was a trend back in 04-09ish where we players went out of our way to add weight to our guns so simulate real weapon weight.

A better question to ask is what is a more durable design for a body.

A pot metal AK receiver is stronger than a M4 receiver due to its shape (rectangle) and the design of the rifle, likewise a mp5 is a better 'shape' for a combination metal / plastic / polymer receiver. If you want a rugged airsoft gun AK's are typically better for that job than M4s. Low end metal AKs (CYMA) are far more rugged than a high end G&P m4 body or vfc for that matter.