In somewhat related news, the Army just cancelled the Improved Carbine program saying none of the submitted rifles met the minimum criteria for continuation. The contenders were FN FNAC (SCAR), HK 416A5, ACR, ADCOR Bear, Beretta ARX160 and Colt Enhanced M4. All contenders were piston designs.
The Army wanted to see 3,600 mean rounds between stoppage with M855A1. According to Army data, the current M4 does 1,691 MRBS with M855A1.