Law enforcement often benefits from the trickle-down effect when it comes to military technology and weapons. U.S. service branches often implement high-priced technology first that then flows into police service.

Examples of this trend include night-vision, thermal imaging, and the AR-15 rifle. The full-length AR-type rifle has now become widespread in police work. The same can be said for the M4-style carbine—its shorter-barrel-length sibling. The M4 carbine traces its lineage to the M16A2 battle rifle—it's a shorter, lighter weight version. Typically, the M4 carbine fires 5.56mm NATO ammunition and has a barrel no longer than 16 inches. The law enforcement version takes .223-caliber rounds.

The M4 has become the U.S. Army's standard-issue combat rifle, and it's also a popular choice for SWAT operators, patrol officers, and federal agents. And it looks like law enforcement will continue to choose it for some time to come.

News broke earlier this month that the Army canceled its Improved Carbine competition. In other words, soldiers will continue using M4s rather than the next-gen carbine Army leaders hoped to hand to their troops.

The Army has reportedly spent $1.8 billion over several years developing the next carbine, reports Bloomberg . Testers have fired hundreds of thousands of rounds through carbines submitted by gun makers such as Heckler & Koch, FNH-USA, Remington Defense, Adcor Defense, and Colt Defense.

Political headwinds in Washington, D.C., appear to be grounding the initiative. The Pentagon plans to reduce Army ground forces to 490,000 by 2017 from about 560,000 in 2011, a top official told a House committee considering defense cuts.

The House Committee on Oversight and Government Reform will most likely reprogram the $49.6 million requested in the proposed fiscal 2014 budget to buy 30,000 improved carbines, reports Military.com .

So for now, military soldiers, as well as law enforcement officers, will have to make do with the M4 carbine for close-quarter battle and other engagements. That may not be such a bad thing.