The U.S. Special Operations Command recently posted a Request For Information Sources Sought Notice to industry for a very particular conversion kit for SIG Sauer MCX Rattlers

SOCOM-- which earlier this year for up to $5 million worth of "Reduced Signature" PDW weapons in the form of modified commercial SIG MCX Rattlers in both 5.56 NATO and .300 Blackout-- posted the notice for 7.62x39mm uppers for the platform in late October. "Due to developing requirements," explains the notice, the force at the tip of the spear is seeking conversion kits to include all "required hardware and ammunition magazines that will fit with the SIG Sauer Rattler and RSAR/PDW converted M4A1 lower receiver groups." 

While, ballistically speaking, a .300 BLK typically outperforms the circa 1940s Soviet-developed round, the obvious ability for SOCOM personnel working in areas where 7.62x39 ammo is widely available to utilize the round could be advantageous. 

Among the details are a 7.75-inch barrel and an overall length of the upper of just 16.4 inches, as well as full compatibility:  


From the SOCOM notice


SOCOM may be in luck as SIG recently debuted their first 7.62x39-chambered offerings in the MCX Spear-LT series. One of the options in that series is a factory SBR with an 11-inch barrel and an overall length of 29.75 inches, something that puts the company within striking distance of the RFI notice. 


SIG Sauer MCX Spear 7.62x39
Of note, the MCX Spear-LT offers AR-15 trigger pack compatibility and runs 28-round mags in its 7.62x39 format. (Photos: SIG)


Either way, we'll keep you posted. 

Banner image: SIG Rattler variant seen at the 2019 Army Expeditionary Warrior Experiments at Fort Benning (Photo: U.S. Army)

revolver barrel loading graphic