This initiative started around 2009, with a 300WM variant of the M240B that was fraught with peril (disintegrating links don’t like belts). Various companies have been working on it for almost 15 years, and the guns are pretty great at this point.
The original 338NM belt fed was a General Dynamics program, there was also a mini gun intend to replace the GAU-19 .50BMG Gatling gun in certain ground/rotary wing applications. I fired about 2000 rounds from the GPMG version…all manually linked match ammo, I believe factory 250gr Scenar Lapua loads.
The 10 200rd belts were probably $10,000…