At this point there is very less detailed information to make a detailed comparison.
What I can say from the apparent features are this:
1> Both are based on the AR-15 design philosophy
2> Both use the short stroke gas piston operation, which is way more cleaner and more efficient than the direct gas impingement system of the M16
3> The MCIWS is multical, which means just by changing the barrel and the bolt assembly, you can get a new weapon. HK-416 only has 5.56 capability where you need the HK-417 to fire 7.62
4> 416-A5 has a gas regulator which enables it to be used with a suppressor. We have no idea yet if there is a gas regulator in the MCIWS. In fact it looks like it has a auto regulating gas piston. Anyway, since the MCIWS is an AR and not a carbine, there is no use of a suppressor for it. CQB/PDW roles would be delegated to the MSMC which can be used with a suppressor.
5> The 12 o'clock P-Rail on the MCIWS is not full length like the HK-416, so mounting multiple optics would be an issue (like reflex+magnifier). Then again such situation arises with SF who uses the TAR-21 anyway. MCIWS is an infantry issue AR which would not need multiple optics.
6> I did not see any bolt release or forward assist on the MCIWS (which doesn't mean it is not there), whereas the same on the 416-A5 is pretty ergonomical and ambidextrous.
7> One of the biggest USP of the HK-416 is it's "fire under any condition" (dirt/water/mud/sand). We would have to wait for trials to know where the MCIWS stands.
8> A proprietary feature of the 416 is its burst mode trigger group, where out of a 3 round burst group, if you fire only 1 or 2 rounds with a short trigger pull, on the next trigger pull, instead of firing just the remaining rounds of the earlier burst group, it resets the counting cam and fires a complete burst of 3 rounds. We do not know if such a feature is incorporated in the MCIWS.
9> Both does not have ambidextrous brass ejection, but the 416 has forward ejection (not to be confused with the F2000 type forward ejection channel) which the MCIWS does not. So a hunched up left handed shooter might have hot brass ejecting on his body, or on his buddy next to him.
10> The 416-A5 weighs between 3.5-3.9kg depending on the barrel length. We do not know the weight of the MCIWS.
@arnabmit, can you compare the design to the HK-416 and point out features/similarities/differences.
Thanks