AR-15 Quad Rails: Best Practices for Upgrading

Silver AR-15 Rail on a white background

One of the biggest reasons AR-15s are so popular is their customizability. And one of the most popular components to upgrade? The handguards.

You see, AR-15s usually come with basic plastic two-piece handguards. Replacing these handguards with a quad rail lets you mount accessories such as lasers, bipods and flashlights.

So what are things to think about when it comes to these quad rail upgrades? Let’s go over a few best practices.

Two-Piece vs. Free-Float

Two-piece rails are the easiest to install. You simply:

  1. Remove the plastic handguards by pushing the delta ring towards the receiver.
  2. Lift off the pieces.

Sounds easy, but the spring behind the delta ring is strong. You need three hands, a friend or a handguard-removal tool such as Promag’s AR-15 and M16 forearm removal tool.

The new rails are a direct replacement for the plastic handguards.

Free-float rail systems require more work. They are usually one complete piece that mounts to a replacement barrel nut. No part of the rail touches the barrel. This helps with cooling and accuracy.

You will usually need to remove the flash suppressor, front-sight post or gas block, gas tube, delta-ring assembly and barrel nut.

This would be a great time to replace any part of your upper assembly like the barrel, flash suppressor, gas block and front sight since you would be removing everything.

Tools required to install a free-float system include:

If you acquire all of the tools necessary to install a free-float rail system, you also have all of the tools necessary to build your own upper from scratch.

Be prepared to have all of your shooting buddies bring you their rifles to install their rail systems. It is easy to do with the proper tools.


Geissele AR-15 Quad Rails Free Float
This Geissele free-float rail is a high-quality addition to your AR-15.


What Size Handguard Do I Need?

For the most part, AR-15 uppers have three different sizes:

  • Carbine
  • Mid-length
  • Rifle length

For the handguards:

  • Carbine lengths are 16” or less
  • Mid-length are usually found on 16” to 18” barreled uppers and use a mid-length gas system
  • Rifle length handguards fit on a 20” barrel

For the rails:

  • Carbines take 6-3/4″ rails
  • Mid-length take 8-1/2″ rails
  • Rifle-length rails are 12” long

Exceptions are Colt carbines, which are 6-7/8” long. Either way, when it comes to AR-15 quad rails and handguards, size matters.

Leapers AR-15 Light
Adding a handguard with rails allows you to attach tons of lights, laser and other accessories to your AR-15.

Covers vs. Ladders

Once the rails are installed, they look great, although are not exactly comfortable to grip. The sharp edges of the rail can cut or rub your hand the wrong way.

Because of this, many AR-15 owners use rail covers or ladders to protect the rails and their hands when shooting.

  • Covers completely cover the rails and offer the most protection.
  • Ladders fill in the portion between the rails, providing some comfort and protection, but are not quite as bulky as covers.


AR-15 Rail Covers
These rail covers will help make your quad rails more comfortable to grip while firing.

Have any tips for upgrading AR-15s with quad rails? Let us know in the comments section below!

Editor’s note: This post was originally published in December of 2010. It has been completely revamped and updated for accuracy and clarity.

About the Author:

Alex Cole

Alex is a younger firearms enthusiast who’s been shooting since he was a kid. He loves consuming all information related to guns and is constantly trying to enhance his knowledge, understanding, and use of firearms. Not a day goes by where he doesn’t do something firearms-related and he tries to visit the range at least a couple of times a month to maintain and improve his shooting skills.

His primary focus is on handguns, but he loves all types of firearms. He enjoys disassembling and reassembling firearms to see how they work and installs most of the upgrades to his firearms himself, taking it as a chance to learn. He’s not only interested in modern handguns and rifles, he appreciates the classics for both historical value and real-world use.
The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (4)

  1. In addition to quad rail hand guards you can use hand guards with a Key Mod or M-Lock system. These only have Picatinny rail on the top. The rest of the hand guard uses the Key Mod or M-Lock accessory system, whichever you have chosen. These are smoother to the touch and don’t require bulky covers Th be comfortable, but they also allow you to attach additional accessories or Picatinny sections wherever you want them.

  2. One detail that’s not mentioned is timing the barrel nut. When fully tightened down, the top handguard rail may not line up with the rail on the upper receiver, and/or it may be difficult or impossible to slide in the gas tube. This is a timing issue, and is likely to happen when installing aftermarket upgrades. Don’t try to force it to line up by overtightening. If you ever need/want to take it down again you will hate yourself, and probably damage the threads on your receiver. The right way to fix a timing issue is to insert shims (very thin spacer rings) up into the barrel nut before installing. Usually takes 1-3 depending on how much the timing needs to be adjusted. Then you can tighten to the appropriate torque and line it up nice and neat.

  3. Quad rails and covers add needless extra weight. Just get a MLOK or KEYMOD hand guard and add rail pieces if and where you need them. I sold and replaced my quad rails years ago

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