Due to developing requirements… *wink*
Via: The Warzone:
American special operators who are issued new short-barrel Sig Sauer Rattler personal defense weapons, or PDWs, may eventually be able to fire Soviet-designed 7.62x39mm ammunition from those guns. U.S. Special Operations Command says has an interest in buying 7.62x39mm caliber conversion kits for the weapons, which are already set to be able to be configured to fire .300 Blackout cartridges or 5.56x45mm rounds.
“Currently, the RSAR/PDW system is chambered in both the 5.56 NATO and .300 Black Out calibers,” the contracting notice says. “Due to developing requirements, USSOCOM is seeking 7.62x39mm upper receiver caliber conversion kits that are compatible with the SIG SAUER Rattler Lower Receiver.”