Beginners' Guide: M4 Walkaround

Flash Hider / Muzzle Device

The flash hider/muzzle device is found at the tip of the barrel and attaches to the barrel threads. With the exception of Tracer units, sound amplifiers, and suppressors, muzzle devices are purely for aesthetics and do not affect the function of your M4. What they do, however, is make your setup look unique, and can help your build lean into the particular design aesthetic you are seeking, be it standard Military, competition shooting, or Special forces. Other Muzzle devices, such as Tracer units, sound amplifiers, and suppressors are also available and can be installed as a replacement for your standard flash hider. For more information on flash hiders, muzzle breaks and sound amps see our Buying Guide, or if you like the idea of the sneaky look, check out our guide on Tracers and Suppressors.

Outer barrel

The outer barrel is the externally visible barrel. It often follows a realistic profile to keep the weapon looking faithful to the real deal, and in most cases has threads on the tip for a flash hider/ muzzle device and pin recesses for a Front sight/Gas block to be installed. Outer barrels can be extended using threaded barrel extensions and can be replaced on most AEGs with an AEG spec. outer barrel, should you want to change the look of your gun.

Gas Block 

The gas block is the part of the real M4/AR15 which routes the gasses from firing into the gas tube, and back to the bolt carrier to cycle the action. For obvious reasons, the Airsoft gas block is purely an aesthetic choice, but can also help stabilise the barrel nut and prevent wobble or rotation in the handguards.

The M4A1's gas block includes an integrated front sight post, forming the familiar AR15 triangular front sight. Various styles of gas block are available, including types with integrated flip-up sights, Picatinny rails, and low-profile gas blocks which are designed to sit beneath the handguard, giving the AR a sleek and slim profile.

Gas Tube

The gas tube takes the form of an aluminium rod in Airsoft M4/AR15 rifles, as having an actual tube is not necessary, given the way our guns work. This part sits between the gas block and the upper receiver, just above the barrel. Like the gas block, this part is included purely for aesthetics and realism and is not always present on Airsoft M4/AR15s.

Handguard Cap

The Handguard Cap is a simple cap for the front end of the handguard, keeping two piece units together. The modern handguard cap is circular and has two cutouts on its lower circumference to allow for the mounting of an M203 Grenade launcher. Earlier variants omit the M203 cutout, and the M16A1 variation is triangular in profile. A handguard cap is not necessary for an M4/AR15 with a free floated handguard, and is only present when combined with the delta ring.

Handguard / Foregrip / Rail System

Also known as the "Foregrip", the handguard on an AR15 is mounted using one of two methods of attachment; Either Delta ring or Free floated. Delta ring attachment is the basic method provided on the original M4A1 carbine as well as the L119A1 SFW. Handguards which attach to the Delta ring can be swapped out with railed handguards in an instant, with no tools necessary. Whilst the Delta ring allows quick swapping of handguards, easy battery installation in front wired Airsoft replicas, and provides a solid feeling front set, this comes at the cost of weight, and the possibility that bumping the handguard could cause the barrel to become loose, affecting accuracy.

Free floated handguards have the advantage that they do not come into contact with the outer barrel, and as such any force exerted on a free-floated handguard cannot cause the barrel to shift and negatively affect accuracy. A free-floated handguard can also be great for a sleek, high-speed look, and are often lighter when compared to a Delta ring/Handguard Cap/Handguard setup. If you have a Delta ring or Free float setup and wish to change to the other method, it can be done with relative ease but will require an AR15 Armourers wrench. For more information on handguards, rails, and attachment methods see our guide on Rail Systems.

Delta Ring / Slip Ring

The Delta ring, also known as the "slip ring" by old farts, is a Delta profiled circular ring which surrounds the barrel, and usually comes with its own integrated barrel nut and a spring between the two. The Delta ring works together with the Handguard cap and sandwiches the handguards between the two parts. The Delta ring can be pulled back against its spring to release either the upper or lower handguard.

"Slip ring" is often used as an alternative name for the Delta ring, though the term actually refers to the early equivalent to the Delta ring, found on the M16A1 and XM177, which was straight in profile.

Barrel Nut

The barrel nut is a threaded nut which attaches the barrel to the upper receiver and can be several different designs, depending on the choice of handguard. The most common type, the spiked barrel nut, facilitates the attachment of free-floated handguards and can be attached and removed with an AR15 armorers wrench. Most aftermarket handguards will come with the appropriate barrel nut included.

Receiver / Body

The receiver of the M4/AR15, also known in Airsoft as the "body" comprises of two parts; The upper receiver, and the lower receiver. The word "receiver" is derived from its function, as it receives the barrel, internal components, magazine, and stock; comprising of all the fittings needed to tie the whole firearm together. On the real AR15, the upper receiver houses the pressure-bearing parts such as the bolt and bolt carrier, and the lower receiver houses the trigger group. 

Upper Receiver - 

Ejection port  

The ejection port is an opening in the upper receiver through which spent shells are ejected on a real M4/AR15, or on the Rare Arms CO2 GBB AR15. On the majority of Airsoft M4/AR15 rifles, this is where you will find your HOP adjuster, sometimes hidden behind a mock bolt carrier which will need to be retracted using the charging handle before the HOP can be adjusted. If you need some advice on how to set your HOP unit and get the best range and accuracy from your M4, check out our guide on HOP up here.

Dust Cover

The dust cover takes the form of a plate which covers the ejection port and can be flipped down by pulling the charging handle, in most cases. This serves the same purpose in a real M4 as it does in Airsoft; to protect the internals from dirt ingress, reducing the need for cleaning/maintenance, and increasing reliability. The real AR15 has tight tolerances for improved accuracy and stays reliable by simply not allowing debris into the system, rather than loosening tolerances like the AK platform. 

Forward Assist / Bolt Closure Assist 

The forward assist is located on the right side of the upper receiver, taking the form of an angled extension with a button on the end, facing the shooter. On a real M4/AR15 this part is intended to help push the bolt into battery in the event that the cartridge in the chamber does not seat all the way. This part is not present on some older Vietnam Era AR15s, as well as some more modern AR rifles, due to the general consensus that using this device will only make a stoppage worse. This part is purely for aesthetics on the majority of Airsoft M4/AR15s, with the exception being ICS M4 AEGs, with which the forward assist can be used to decompress the spring after firing.

Carry Handle - Fixed / Removable

The carry handle of the M4/AR15 is used as an alternative to carrying the rifle by its handguard or pistol grip. The carry handle also provides a rear ghost ring aperture iron sight and takes two basic forms. The removable carry handle is often provided with M4s with railed receivers and can be easily detached using the two large nuts on the left side of the handle. These sights usually have an integrated A2 style rear sight which is adjustable for both windage and elevation. 

The fixed carry handle is usually found on old-school ARs, such as the M16A1, M16A2, and XM177. In the case of the A1 fixed carry handle, the sight provided within is an A1 style ghost ring, which is adjustable for windage only. With A2 style fixed carry handles the windage and elevation adjustable A2 style sight is integrated into the design. The difference between this and the removable carry handle is...you guessed it! The fixed carry handle is a part of the upper receiver, and cannot be removed. Fixed carry handles can, however,  accept 20mm railed mounts so if you want that Blackhawk Down style look for your old-school AR, it can be done!

Charging / Cocking Handle

The charging handle can be found at the top rear of the upper receiver, and on the real M4, this part impinges on the bolt carrier and is used to cock the rifle. In Airsoft, this part tends to be for aesthetics only, often providing access to the HOP chamber for adjustment by holding the dummy bolt carrier to the rear. The standard AR charging handle has a release catch on the left side and is optimised for right-handed use, though aftermarket charging handles are available with ambidextrous functionality.

Lower Receiver -  

Magazine Well

The magazine well is the part of the lower receiver into which you insert your magazine. All M4/AR15 magazine wells are very similar in profile, though some are available with gripping surfaces on the outside, cut-outs to reduce weight or reangled flare at the bottom of the mag well, to assist in speedy reloading. The magazine well is also where you will find the M4/AR15s manufacturer trademark, and serial number. 

Pistol Grip

I think we all know what this is, and what it does! The pistol grip, also known as the hold-y on-y bit, is where you grip the rifle, is conveniently located next to the fire controls and can be found attached to the lower receiver. Airsoft M4/AR15 grips are widely interchangeable, and come in two specs; AEG and GBBR spec. Most AEGs can take an aftermarket pistol grip intended for AEGs, though there are some which use their own unique style of pistol grip. If you are ever unsure as to whether you can swap your pistol grip for an aftermarket one, get in touch and we would be happy to advise. 

Fire Mode Selector / Selector Switch

The fire mode selector, also known as the selector switch is a rotating switch which provides 3 positions, generally for Safe, semi automatic, and fully automatic on most M4/AR15 rifles. Some M4/AR15 rifles have the ability to program the semi and full auto position for bursts of different duration. The M4/AR15 selector switch has a 90 degree throw between fire modes. This switch is usually found on the left side of the lower receiver, just above the pistol grip. Being positioned on the left side allows the selector switch to be used with the thumb for a right-handed shooter, or the trigger finger for a left-handed shooter. Ambidextrous selector switches are also found on certain M4/AR15 variants, providing an additional fire selector on the right side of the lower receiver. 

Magazine Release / Catch

The magazine release is a push-through design, found installed into the lower receiver and accessible from the right side of the receiver. This button is usually actuated by the trigger finger for a right-handed user and with the thumb of the reaction hand for a left-handed shooter. Ambidextrous magazine releases are available and can be swapped with the standard magazine release on the vast majority of M4 rifles, allowing a left-handed user to release the magazine with their firing hand. 

Buffer Tube / Stock Tube / Receiver Extension

The buffer tube, also known as the stock tube, is the cylindrical pipe at the rear of the M4 receiver, to which your stock mounts. This is also known as a receiver extension. The original XM177/CAR-15 buffer tube had only two positions, fully extended or collapsed. When the M4A1 first dropped, the buffer tube had 4 positions, and modern day variants have 6 positions. The buffer tube provides the widest variety of stock options for the M4/AR15 platform, being compatible with nearly every stock on the market, with few exceptions. The standard buffer tube can be exchanged for a full stock, slimline competition-style tube stocks, or UBR/M93 style stocks. 

Sling Plate / Receiver Plate

The receiver plate, also known as the sling plate, is a flat plate which seals the back end of the lower receiver, being secured between the buffer tube/castle nut and the rear of the lower receiver. These plates often include sling mounting apparatus, including sling rings, bars and QD sling sockets. If your M4 AEG has a basic receiver plate it can be easily replaced with a sling plate; First, remove the buffer tube, then remove the old plate, pop your new plate on, and tighten the buffer tube down on top. 

Castle Nut 

The castle nut is a threaded nut which secures the buffer tube to the lower receiver and comes in the form of a large nut with cutouts for an AR15 armourers wrench. The name comes from its shape, appearing similar to a castle tower with crenelations on top. On most AEG M4/AR15s, these are cast as a part of the buffer tube, but on Tokyo Marui NGRS, Systema PTW, and GBB M4/AR15s the castle nut is a separate piece and works the same way as it does on a real AR. 

Stock

We all know what a stock does, or we should do by now! The M4/AR15 stock is one of its most modular parts, with a wealth of aftermarket replacements available to suit any style, colour scheme or tactical need. The majority of M4/AR15 stocks attach to the M4 buffer tube, and can be removed and swapped as quickly as they can be adjusted between positions. These stocks offer adjustment of length of pull and can often have cheek risers and rubber recoil pads/butt plates added. The M16 full stock is another option, providing a large battery compartment and a more solid, 100% wobble-free solution for those with longer arms or those not wearing body armour. The M16 stock does not require a buffer tube to attach to, it attaches directly to the lower receiver instead of the buffer tube, and comes with its own receiver plate. Solid stocks are not compatible with sling plates intended for buffer tubes, and usually provide a sling loop, or QD sling sockets, keeping your sling options open. For more information on stocks in general, check out our Stocks Buying guide here.