These photos, showing the upcoming 7.62x39mm version of the SIG556, is purportedly straight from SIG Sauer.
They are using the SIG550 (aka. Classic) forend and sidefolding stock. Troubleshooter, a reader of the blog, emailed me to say that lower receiver is similar in contour to the 5.56mm version and therefor the deep magwell (deep compared to the AK) probably prevents AK-47 drum magazines from being used.
[ Many thanks to Troubleshooter for emailing me the info. ]Related