M16 to M4 – Technical Specs

M16

Materials

Primarily, the materials used in the production of the M16 were aluminum and plastic. The bolt carrier section, barrel, and trigger are made of steel. Fiberglass construction is also used where wood was once used, making the rifle even lighter than any of its predecessors.

Rifling

Commonly, the rifling on the M16 and its many variants is between 1:7 (1 turn in 7 inches) and 1:12. Depending on the range of targets and the ammunition used, the ideal twist rate will vary. For heavier bullets, a more rapid twist (closer to 1:7) is needed. For lighter bullets, a 1:12 twist rate should suffice.

M4

Ballistics experts agree that the desired twist rate is 1:7 or 1:8. While this is a fast twist, which can accommodate all kinds of ammo, it comes with a price. The faster the projectile turns, the faster the barrel becomes dirty with build-up.

Each model of rifle in the extended AR-15 family has a unique twist rate. You won’t find two of the same model with different kinds of twists, unless the barrel has been replaced with that of a different model.

Originally, the M16 rifle had very different rifling: right-hand twist, 4 grooves, 1:14. Later, the grooves became 6. Currently, the twist is 1:7. Civilian M16-dopplegangers have a twist rate of 1:9.

The M4 rifle has a right hand twist 1:7

Sights

The sights on the original M16 were assembled as part of the carrying handle. There was a time when a scope would be mounted on the handle itself.

The M16 rear sight is adjustable, with two setting: 0 – 300 meters, and 300 – 400 meters. Many soldiers were trained to fine tune their weapons using a cartridge. The M16A2 brought with it an important advancement: the rear sight became fully adjustable, without the need for a tool or bullet tip. In later models, the M16 already comes with picatinny rails, and it allows for different scopes and optic accessories to be attached.

The United States Armed Forces use different types of optics for the different military branches:

The current United States Army and Air Force issue M4 Carbine comes with the M68 Close Combat Optic and Back-up Iron Sight.

The United States Marine Corps uses the ACOG Rifle Combat Optic, and the United States Navy uses EOTech Holographic Weapon Sight.

Magazines

M16 cartridge magazines

The M16 cartridge magazines were meant to be for one time use. In the beginning, when there was a 20-round magazine, troops would only put in 16 cartridges, in order to avoid harming the magazine spring. When the magazine capacity grew to 30 rounds, the troops would put in less rounds for the same reason.

The M16 magazine is another set standard by which many other magazines are measured and judged. It is made of pressed or stamped aluminum, it has a bent shape, and it is very lightweight. This causes some problem on occasion, which is why other gun companies and weapons manufacturers have taken to produce more durable, high-quality, less malfunction-prone M16 magazines.

Since its inception, the design of the M16 magazine has been copied and used in all kinds of weapons systems all around the globe. It is still one of the most popular magazine designs in the world. There are steel magazines, as well as plastic ones.

Muzzle Additions

Many M16s have a threaded barrel, which allows the incorporation of devices such as flash suppressors and sound suppressors. Originally, the M16 had a three-pronged flash suppressor, but there were complaints of the suppressor breaking or getting stuck in vegetation. The M16A1 was made with a “bird cage” flash suppressor, and the A2 was made with a “bird cage” and a closed bottom. This was done to avoid dust and dirt being kicked up by the rifle’s action. The United States military currently uses Vortex flash suppressors, designed and created in 1984, by Smith Enterprises.