must be a really heavy barrel....
"– Gas settings changed from Off/Normal/Adverse to Suppressed/Normal/Adverse
– New removable hand guard, including rail, Mlok, and UBGL versions
– Strengthened stock attachment
– Heavier barrel
– Replaceable cam lug rail in the receiver
– 7.62×39 chambering replaced by .300 Blackout
– Optional folding charging handle
– Slightly improved stock, and universal compatibility with collapsing “PDW” stock
– Heavier barrel
– Strengthening of various small internal parts"