The change the military made to the M4 extractor was in the polymer extractor spring insert, not the spring itself.
The old style (and still acceptable for current issue in the military) is the blue polymer insert. The newer insert is black in color, and a little stiffer.
From what I understand, the black insert was introduced to ease extraction problems in full auto with the shorter-barreled M4 carbines with collapsible stocks.
Xring and Espring are products of Olympic Arms, not Bushmaster, and do pretty much what the black insert is designed to do, or what the long-standing Armforte' D-Fender extractor insert is designed to do.