HurricanE have added a new M16A1 metal body to their listing today (product code HE-MB-09). The new A1 metal body costs 245USD which is more than the stnadrd M16 body that they make but it does come with more parts.
This new metal frame is deisnged to fir the Marui M16A1/VN、M16A2、and M4A1 series. Included in the package is a forward assist knob, charging handle, new pins, metal hopup, new trigger guard, new ejection port cover, several hopup parts, new outer barrel sleeve and new handguard ring.
The new part is listed as in stock right now, so should be available at your local dealer shortly.