Shoulder Stock----different kind of Shoulder stock.Ak-12 has Stock Latch,while MCIWS has adjustable stock.plus,Ak-12 has Folding Stock as well.Probably,MCIWS will also come with similar folding or smaller folding stock.
Barrel Length-- Ak-12---16.3''
MCIWS--probably 18.3'',similar as INSAS
Holding Front grip--funny,many guns also have similar holding front grip
Fire Selector-- Ak-12--Full Auto or 3 rounds burst
MCIWS-Single and Full Auto
so,it is different
Length-AK-12 is longer
Magazine-- AK-12--it uses various kind of magazines,30-round magazines,45-round magazines,while specifically designed 30-round magazine with bolt-catch actuator, a 60-round quad-stack magazine, and a 95-round drum is under development.7.62 Soviet-chambered version is compatible with AKM/RPK 30-round and 40-round magazines and 75-round drums.
MCIWS-For now,Transparent 30 Round magazine which Insas used.