Estimated reading time: 11 minutes
There are a lot of reasons why you would want to swap out the hand guard or rail on your AR-15. Maybe you want to mount a tactical light, vertical grip, or hand stop and you need a rail that can accommodate those accessories. Or you might want to install the free float variety for better accuracy.
Maybe you use a thumb-over-bore support hand grip and you’re sick of having your thumb get chewed away by a full-length Picatinny rail? Do you want a full-length Picatinny rail to mount a specialized optic? You choose the reason and I’ll walk you through this AR hack. Depending on your current setup this hack is either super easy or just plain easy. First, let’s talk about the two types of hand guards.
Table of contents
Types Of AR-15 Hand Guards
There are a few different types of AR-15 hand guards, but they mostly boil down to either free-floated or not-free-floated drop-in style. The free-floated type does not come in contact with the barrel. In theory, this makes the rifle more accurate because there is no contact to throw off the barrel and won’t interfere with the barrel harmonics.
A non-free floated or drop-in hand guard does contact the barrel. Don’t worry though, for defense work and hunting a drop-in rail will not be an accuracy liability. I’ve shot ARs with drop-in rails out to 1,000 yards with no issues. Service Rifle competitors shoot out to 600 yards with rifles equipped with drop-in guards. The free float does remove any potential impact on accuracy.
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Drop-In
A drop-in AR-15 hand guard is typically a two-piece, polymer with a metal heat shield inside. The two pieces sandwich together. The cap behind the A2 sight and the delta ring on the upper receiver holds them together. These are used on rifles with A2 front sights and are classic military-style hand guards that do not require any modifications to the rifle to install. The round polymer style on an M16A2 is a drop-in. Drop-in AR-15 guards typically come in three lengths: Carbine, Mid-Length, and Rifle. Choose the length that matches the gas system of your gun. A good example of a drop-in is Magpul MOE M-LOK hand guards which are made of polymer with an interior heat shield.
Drop-in hand guards also come in a railed version with four Picatinny rails. These are often called quad rails and are made of aluminum. The rails sit at the 12, 3, 6, and 9 o’clock positions. The downside of these rails is they act like a cheese grater on your support hand after extended shooting sessions. The solution is to use a rubber rail cover to fill up the slots. On the plus side with a quad rail hand guard accessories can easily be added. Midwest Industries, Yankee Hill Machine, and several other manufacturers produce this style.
Free-Float: Railed, KeyMod And M-LOK
Free-float AR-15 guards do not contact the barrel allowing the barrel to float inside. These hand guards help to improve accuracy and come in three styles: Railed, KeyMod, and M-LOK. The railed type has four Picatinny rails located at the 12, 3, 6, and 9 o’clock positions. The advantage of a Railed guard is the ability to accommodate a wide variety of accessories like vertical grips, hand stops, bipods, tactical lights and laser pointers.
A KeyMod hand guard features slots that look like keyholes that allow attachment of accessories. VLTOR developed the KeyMod system. These rails are more slender than a Rail and typically lighter. KeyMod hand guards are the least popular of the three types of free-floats since fewer accessories support the KeyMod system.
Magpul developed the M-LOK, which is the newest type of free float. These feature narrow slots at the 12, 3, 6, and 9 o’clock positions that allow the installation of accessories as long as the accessory is M-LOK compatible. M-LOK hand guards use T-shaped nuts. These have a slim profile and are lightweight. With both KeyLok and M-LOK, small sections of Picatinny rail can be added to gain the benefit of a Railed hand guard. If you are deciding between KeyMod and M-LOK know that testing in 2017 by USSOCOM found that the M-LOK outperformed the KeyMod in drop testing, failure load testing, and repeatability.
Some types combine the features of a Rail and either a KeyMod or M-LOK. Your choice of hand guard depends on factors like mounting options, weight, ease of installation, and intended use of the rifle.
How Do AR-15 Free Float Guards Work?
A free float hand guard attaches to a compatible barrel nut. The barrel nut secures the barrel assembly to the upper receiver. The barrel assembly includes the gas tube and gas block. Since it attaches to the barrel nut it allows the barrel to float or have no contact with the hand guard. The gas tube and gas block also have no contact with the guard. A barrel nut and free float hand guard must be compatible, meaning not all barrel nuts work with all hand guards. Most free floats include a barrel nut. For example, the UTG AR-15 Forerunner 15” M-LOK free float includes a barrel nut and wrench and barrel nut locking screw. It also comes with a small 8-slot piece of Picatinny rail, a QD adapter, and a hex wrench to install everything. This is a good hand guard for a thumb-over-bore support hand grip.
How To Install An AR-15 Drop-In
If you have strong hands you do not need any tools to replace the drop-in. A delta ring tool makes to job a lot easier. You can either pull back the delta ring using your fingers or use the tool. Either way allows the two halves to come apart. Remove the old drop-in hand guard, place the muzzle ends of the new hand guard into the cap, and snap the delta ring over the receiver-facing end of the hand guard. Done.
On some quad rail, there may be screws that hold the two halves together.
How To Install A Free Float Hand Guard On An AR-15
You need a low-profile gas block. The standard diameter of AR-15 barrels is 0.750” so make sure the low-profile gas block matches that diameter. If you are unsure use a set of calipers to measure the barrel. Also, be sure the inside diameter of the hand guard you are installing is slightly larger than the outside diameter of the gas block. You should be able to reuse the gas tube from the A2 sight.
Some Necessary Tools
The muzzle device, A2 front sight which houses the gas block, gas tube, and barrel will need to be removed. This type of swap requires tools: Bench vise, upper receiver action block, barrel wrench, muzzle brake wrench, bench block, ball peen hammer, nylon hammer, 1/8” punch, and roll pin punch. To make this task easier, I use the Real Avid Master Bench Block to punch out the pins in the A2 sight. I also use the Real Avid Armor’s Master Wrench since this tool removes the muzzle device and a mil-spec barrel nut plus it can be used on free float hand guard barrel nuts, the castle nut on the buffer tube, and more. You can also use it as a club when you run out of ammo.
Remove A Few Things
Remove the upper from the lower, place the upper in a vise block, and tighten the vise block in a bench vise. Take off the muzzle device. Remember the crush washer is a one-time use item. You need to replace it.
Knock out the two lower pins in the A2 sight. One end of the pin is larger than the other. The pins are removed by tapping them out from the left side to the right side using a 1/8” punch. Next, remove the sight from the barrel. You may need to use a nylon hammer to gently tap it off. Use a bench block, roll pin punch, and hammer to remove the roll pin that holds the gas tube to the sight.
With the barrel in the upper receiver, hand tighten the barrel nut that came with the free float then use the wrench adapter that came with the hand guard and a torque wrench to tighten the nut to 35 ft.-lb. Do not over-tighten.
Add A Few Things Back In
Install the low-profile gas block and gas tube, and then the muzzle device. Slide the guard over the barrel until it mates up with the upper receiver. Tighten ups the two hand guard screws to a maximum of 15 ft.-lb. Don’t gorilla the screws and over-tighten them. Done.
READ MORE: What’s A Mid-Length Gas System?
Why Install A Free Float Hand Guard On An AR-15?
Changing to a free float hand guard on an AR-15 can increase accuracy and provide a sturdy platform to attach accessories. This AR hack is a little more involved but easy if you have the right tools.
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