Reportedly the 416 was originally called the HKM4, but was renamed in response to a trademark infringement suit filed by Colt Defense. “It is speculated that '416' is a reference to the M4 and M16 it's designed to compete with.”

Design

According to H&K

“High-speed video assessment and extensive live-fire testing in extreme operational environments such as the U.S. Army Desert Proving Ground in Yuma, Arizona revealed multiple areas for improvement of the 5.56 mm carbine. Improvements were made to the internal operating system and miscellaneous component parts to improve reliability in best and worse case scenarios, with all types of ammunition, with all barrel lengths and with and without sound suppressors attached.” - H&K

The H&K416 uses a gas system derived from the H&K G36, replacing the direct impingement gas system used by the standard M16/M4. The H&K system uses a short-stroke piston driving an operating rod to force the bolt carrier to retract. This design prevents propellant gases from entering the weapon’s interior as is the case with direct gas impingement systems. The reduction in heat and fouling of the bolt carrier group increases the reliability of the weapon and extends the interval between stoppages. It also reduces operator cleaning time, and stress on critical components. However, escaping gases when firing the system are noticeable, as they vent from the forearm.

The H&K-416 is equipped with a proprietary accessory rail forearm with MIL-STD-1913 rails on all four sides. This allows all current accessories, sights, lights, and lasers used on M4/M16-type weapons to be fitted to the H&K-416. The H&K-416 rail forearm can be installed and removed without tools, using a bolt locking lug as the screwdriver. The rail forearm is of the 'free-float' variety; it does not contact the barrel. This allows the fore end to be removed and reinstalled without tools, and with no loss in zero

The H&K-416's barrel is cold hammer-forged. This allows the barrel to maintain its accuracy for over 20,000 rounds, with minimal degradation of muzzle velocity. The cold hammer-forging process also allows for improved operator safety during obstructed bore occurrences or after extended firing sessions. This includes "OTB" (Over-the-beach) capability: the H&K-416 can be safely fired after being submerged in water and not completely drained.

Heckler & Koch has also applied Blank Firing Attachment and Live Round Excluder Magazine technology to the H&K-416 Carbine, eliminating the possibility of live rounds being loaded into and fired through a standard issue weapon outfitted for blank firing only.

“Features

• Short-stroke piston gas system
  - Improved reliability
  - 100% function
  - No fouling directed into weapon
  - Less cleaning
  - User removable/exchangeable components
  - Insensitive to barrel length or ammunition changes
• Improved buffer system
• Improved steel magazine:
  - Improved feeding reliability, durability, service life
• Refined barrel/bolt locking recesses/lugs:
  -Improved function
• Improved extractor and spring, buffer:
  -Improved function
• Enhanced AG-C add-on 40mm grenade launcher
• HK cold-hammer forged barrel
  -Extended service life
  -Improved accuracy and user safety
• HK free-floating modular rail system” - H&K
  

The H&K-416 is currently available in four different barrel lengths:

• D10RS (10.4 inch / 264mm )
• D145RS (14.5 inch / 368mm )
• D165RS (16.5 inch / 419mm )
• D20RS (20 inch / 508mm)

Evaluation

In July 2007, the US Army announced a limited competition between the M4 carbine, FN SCAR, H&K-416, and the previously-shelved HK XM8. Ten examples of each of the four competitors will be involved. Each weapon will fire 6,000 rounds in an "extreme dust environment." The purpose of the shootoff is for assessing future needs, not to select a replacement for the M4.”

The Army plans to buy about 100,000 M4s in fiscal 2008, each M4 without accessories costs about $800. As part of the contract, though, each M4 comes with a rail system for mounting optics and flashlights, a backup iron sight, seven magazines and a sling — additions that raise the price for each M4 package to about $1,300, according to Defense Department budget documents.

The price of each H&K-416 “will range anywhere from $800 to $1,425 depending on volume and accessories,” said H&K’s CEO John Meyer Jr. - Article by Wikipedia®