As mentioned by
@Kunal Biswas dada wayyy back in 2013,
http://defenceforumindia.com/forum/threads/successful-user-trial-of-msmc.55979/page-2#post-815509
It is more likely similar to a cancelled project - a carbine (or 'Mini Assault Rifle') and its cartridge designated 5.56 x 30mm MARS,developed by Colt.
Colt MARS -
Mini Assault Rifle System,Chambered in 5.56 x 30mm MARS
.
Colt's 5.56 x 30mm MARS round and its dimensions
Their aim was to make a ultralightweight carbine chambered in shortened 5.56mm cartridge that have similar ballistic performance to standard 5.56 x 45mm round.In that way,they can have a lightweight fully automatic carbine with same barrel (albeit,shorter for carbine role),almost similar parts and mainly,a similar weapon to standard issue assault rifle.This weapon could've become a forerunner of M4 carbine with true carbine round that has almost similar performances to 55 grains standard 5.56 x 45mm upto 300m,not bad at all for a carbine.
This weapon could've replaced many aging M3 'grease guns' as they were still being used by US Armed Forces (mainly,tank crews and SF commandos) in mid 90's and those 9mm MP5 sub-machine guns with more lethal weapon but arrival of M4 carbine,a rifle cartridge carbine might have make it 'unnecessary' in views of US Armed Forces.
Our effort to make a 'Sub Machine Carbine' is similar to this project,We made Amogh in conventional rifle configuration and MSMC/JVPC in 'semi-bullpup' configuration.
For more information,