The SIG Sauer MCX SBR is easily one of the most unique PDW’s on this list because it was designed from the ground up to accept stocks, fronds, and calibers. On top of that, it’s also very lightweight and compact, and comes suppressor ready from the factor. The two position, short stroke piston system is also built by SIG Sauer to help aid in reliably. The upper receiver is steel with a feed ramp insert, charging handle latch point, replaceable forward assist housing, and a camp path plate. Let’s put it this way, the MCX is essentially the ultimate PDW that can do anything any other PDW can and then some.