Different action, different ammo.
Again, until you fire it and have had the engineers discuss it with you, all you have is uninformed opinion.
As I stated before, we'll know soon enough. The M16 series is a spectacularly successful weapons system, esp. in current SOPMOD/MWS configuration and USMC M16A4. SCAR is an incremental improvement, hardly a death ray.
Having them both in widespread combat use will be interesting - were it really a priority it would have been fielded already.
Time will tell if the operators in SOCOM are truly ready to abandon their AR pattern long guns.