Lets face it. The M4 jams...
http://www.defenseindustrydaily.com/the-usas-m4-carbine-controversy-03289/
75th Ranger Regiment member, SOCOM:
“Even with the dust cover closed and magazine in the well, sand gets all inside; on and around the bolt. It still fires, but after a while the sand works its way all through the gun and jams start.”
25th Infantry Division soldier:
“The M4 Weapon in the deserts of Iraq and Afghanistan was quick to malfunction when a little sand got in the weapon. Trying to keep it clean, sand free was impossible while on patrols or firefights.”
82nd Airborne Division soldier:
“The M4 is overall an excellent weapon, however the flaw of its sensitivity to dirt and powder residue needs to be corrected. True to fact, cleaning will help. Daily assigned tasks, and nonregular hours in tactical situations do not always warrant the necessary time required for effective cleaning.”
Sgt. Charles Perales of Fort Bragg, NC had this to say in a letter reprinted by Defense News:
“My unit – B Company, 2nd Battalion, 504th Parachute Infantry Regiment – was deployed to Afghanistan from April 2005 to March 2006. While there, we were attached to Special Forces at Camp Tillman on the Afghan border…. I saw first-hand what happens when your weapon jams up because of the harsh environments we have to call home there. An 18B weapons sergeant was shot in the face due directly to his weapon jamming. I just can’t believe that after things like this happen, the Army is still buying more M4s."