Had this program not been cancelled, the XM8 system may have faced competition from weapons such as from the FN SCAR, Robinson Arms XCR, or H&K 416, all of which can be re-configured to various roles. The U.S military's XM8 program was cancelled in fall 2005 after being suspended earlier in the year. Independent work by H&K on the XM8 has continued. It was altered and entered as a candidate for the SCAR competition but was unsuccessful.
Despite reports to the contrary, the XM8 is not dead. In July 2007, the US Army announced a limited competition between the M4 carbine, FN SCAR, HK416, and the previously-shelved HK XM8. Ten examples of each of the four competitors were involved. Each weapon had 6,000 rounds fired in an "extreme dust environment." The purpose of the shootoff was for assessing future needs, not to select a replacement for the M4. [1] The XM8 scored the best, with only 127 stoppages in 6,000 total rounds [2], while the M4 carbine had 882. The FN SCAR placed second with 226 stoppages, and the HK416 had 233. The difference between the XM8, HK416, and FN SCAR was statistically equivalent when correcting for the less reliable STANAG magazine.
The competition was based on two tests that were conducted in 2006 and in the Summer of 2007 before the latest test in the Fall of 2007. In the Summer 2007 test, additional lubrication was credited with "drastically improving" the M4's performance over the initial 2006 test which involved both M16 rifles and M4 carbines, scoring a total of 307 stoppages. The Fall 2007 test was also conducted with the additional lubrication used in the Summer 2007 test but resulted in 882 stoppages.
This discrepancy of 575 stoppages is so large that it has thrown the validity of all three dust chamber tests into question. Army officials are looking into possible causes for the change such as different officials, seasons, and inadequate sample pool size, but have stated that the conditions of the test were ostensibly the same, which points to the test itself as being non-reproducible and invalid as a scientific platform for evaluation of the rifles