The thing to keep in mind is that this test was only run to humor a Congressman, and are not part of any solicitation for a new service rifle or carbine. I suppose the issue could become enough of a political football that Congress could order the US military to open bidding for, and adopt, a new rifle, but I don't suspect that's likely unless some Democratic hopeful wants to try and make some political mileage off the issue.
As a comment, there are two fundamentals with procurement spending; maximize dollars to the contractor and avoid scandals.
What likely happened before the test results were made public was that Colt and the Military M4 Project Manager were given a “read ahead” copies. In defense procurements the military becomes the advocate for the Contractor. So both Colt Lobbyists and the M4 Project Manager were probably on the Hill doing preemptive damage control. The Military Project Manager is fighting the battle with view graph technology, Colt Lobbyists are doing the same but with sweeteners: campaign contributions. Campaign contributions are extremely powerful motivators on Capital Hill. If the Rep. Randy “Duke” Cunningham “Bribe to Benefit Ratio” holds true, about $100,000 of campaign contributions will buy you $100 million in defense contracts. Without a doubt Colt lobbyists have been dropping sugar plums of $10K, $50K contributions in the offices of Strategic Congressman, with the promises of more.
Once a contractor is being fed from public tax dollars, it is extremely difficult to cancel or divert the money. In this case, you have this corporate entity, Colt, that has at least $375 million of M4 procurement dollars to use to defend their cash flow.
Considering that any replacement rifle will not be a revolutionary advancement over the existing rifle, and the amount of non tax payer dollars it would take to buy sufficient Congressman to force change, well you can bet that nothing substantive is going to happen.
There will be some hand waiving. Some improvements, like a new paint job. Or maybe a committee will be set up to make recommendations.