If 5.56 is obsolete,
It is obsolete according to experience on the battlefield and the Small Arms Survey.
The service has been employing its standard-issue M4 carbine since the 1960s while steadily making improvements to the system over time. But now, the rifle’s 5.56 mm round may not be able to penetrate enemies’ newly developed body armor, officials said.
During a Senate Armed Services airland subcommittee hearing last year, Sen. Tom Cotton, R-Ark., noted that “everyone from Russia and China, to Hezbollah” and the Islamic State is employing advanced armor that “risks making the 5.56 round essentially obsolete.”
https://www.nationaldefensemagazine.org/articles/2018/2/1/pentagon-takes-new-look-at-rifles-ammo
“Right now, the feedback looks like we are going to a 6.8 mm round,” Army Chief of Staff Gen. Mark Milley said recently.
The service has a list of its top six modernization priorities and “soldier lethality” is one of the items. The most high-profile program in that category is the squad automatic rifle. Army Secretary Mark Esper at the Association of the United States Army annual conference — while promising the service is speeding up the way it does acquisition — singled out the program as one that would see prototypes in the near future.
“The bottom line is that we are committed to a new rifle,” Milley told reporters.
https://www.nationaldefensemagazine...army-serious-about-fielding-6-8-caliber-round