Tactical Life posts that the military is changing to the 6.8 in SAW and M4

[LRRPF52]

They're working on a 125gr .277" EPR projectile with a stated goal of shooting it at 3500fps from a 16" barrel.

Not even a 26" .270 Winchester will do that, and the .270 works at 65,000psi with 63gr of case capacity.

1923-1932 (Experimental) .276 Pedersen Garand Cancelled
SALVO Various Experiments led to numerous cancelled programs
1951-1968 SPIW (Special Purpose Individual Weapon) Cancelled
1955 M14 Adopted (for a few years, then replaced immediately with the AR15)
1959 M60 Adopted
1974 6mm SAW Cancelled
1980 SAW M249 Adopted
1986 ACR (Advanced Combat Rifle) Cancelled
1994 M4 and M4A1 Adopted
1997 M240B Adopted
1995-2000s OICW testing and development of Hk XM29 Cancelled
2003 Hk XM8 Cancelled
LSAT......????
2017 ICSR 7.62 NATO rifle Cancelled
2018 6.8 EPR 3500fps 16" barrel..........

All of the small arms programs that were overly ambitious in terms of technical ability, major technology developmental hurdles to overcome, with large RDT&E budgets ended up being cancelled. Look at the SPIW, OICW, and even the ACR (which had caseless ammo introduced by Hk with the G11).

Many of the reasonable designs that didn't represent significant technical challenges weren't adopted either, like the .276 Pedersen Garand (a superior chambering for an infantry rifle), 6mm SAW (this would have been a much better SAW cartridge with tangible armor/barrier defeat and effective range increases), or Hk XM8.

The technical challenges of making a shoulder-fired rifle/machinegun launch a 125gr solid EPR at 3500fps from a 16" barrel and still remain lightweight, with low recoil, and a long-lasting barrel/action is huge, some would say completely unrealistic.

Chances of it being successful in the light of previous programs and the engineering challenges associated with it project it as an almost guaranteed failure from the start.