Which Rail is Right For You?

The Purpose of a Rail

The rail or “handguard” of an AR15-style rifle serves three main purposes:

1.       It protects your hand from a hot barrel

2.       It provides a secure purchase for your support hand to steady and maneuver the rifle

3.       It provides real estate to attach accessories, such as lights, optics, sling mounts, and more

Rails also just plain look cool and enhance the aesthetic of your firearm, but that’s not a purpose so much as an added benefit.

"Drop-In" vs "Free-Float" Rails

How a rail attaches to a firearm determines which style it is, and the two basic styles are:


Drop-in rails are classic, two-piece systems that got their name because installing or removing them typically involves pulling back on a spring-loaded ring and “dropping” them in.

There are several advantages to drop-in rails, including but not limited to:

  • They’re usually easy to install and uninstall
  • They’re typically less expensive
  • You don’t generally need to make any modifications to an AR15-style rifle for them to fit properly


A free-float rail mounts directly to the upper receiver so, unlike a drop-in rail, it does not touch the barrel. This means it doesn’t affect a barrel’s harmonics, perhaps the biggest selling point of free-float rails.

Daniel Defense rails are all free-floating because accuracy matters and much of the company’s reputation is based on manufacturing highly accurate firearms, so the rails attached to them should never take away from that.

The Big Three Attachment Systems

Once you’ve decided how your rail is going to attach to your rifle, it’s time to decide how you want accessories to attach to your rail. There are three primary styles of rails, and they differ mainly in how accessories attach to them.

1913 Picatinny:

This type of rail has been around the longest and is a tried-and-true classic design. It is basically a series of ridges with a cross section shaped like a T and flat slots spaced between them. Accessories fitted over these ridges and into the slots and attached via bolts, thumbscrews or levers.     

  • Advantages: This type of rail provides secure attachment, and it is ubiquitous, so just about any accessory can be acquired with a Picatinny-style mount. Because the rail itself has the least amount of negative space of the three types—meaning the least amount of material cut away—it is also the heaviest and typically most robust system. While being heavier can definitely be a disadvantage, it can also be advantageous if an attached accessory needs to hold zero (like an optic) when mounted and the rifle hosting the rail gets banged around or subjected to harsh conditions.
  • Disadvantages: As mentioned, being the heaviest rail system, it can make your rifle heavier and, consequently, more difficult to maneuver or carry all day—especially if the rail is loaded down with accessories. It’s also the most angular style of rail, so it can be tough on bare hands. While you may want to wear gloves with any rail for protection from heat, gloves with a Picatinny rail can also help prevent cuts or abrasions from sharp edges.   


This type of rail accommodates accessories by inserting an accessory’s mounting nuts through the large holes of key-shaped slots (which resemble slots in industrial shelving) in the handguard. You then slide the accessory forward, into the smaller front portion of the slot, and tighten the mounting bolts.

  • Advantages: KeyMod rails are typically significantly lighter than Picatinny rails because they feature more negative space, which means less material making up the rail. Accessories attached via KeyMod also don’t protrude as far into the rail as they do on an M-LOK rail, so a KeyMod rail can fit snugger and be closer to the barrel. This can be advantageous on firearms with very little clearance between the barrel and rail.
  • Disadvantages: In head-to-head testing by the Naval Surface Warfare Center, Crane Division done in 2016, M-LOK fared better in categories such as repeatability, endurance, rough handling, a drop test, and failure load. KeyMod took a significant hit in popularity after this test report came out, but the system is far from dead. But, because it’s not as popular as Picatinny or M-LOK, it can be more difficult to find accessories using KeyMod attachment. Also, unlike Picatinny attachment, attaching an accessory to a KeyMod rail requires special tools.


Like KeyMod, M-LOK utilizes more negative space than a 1913 Picatinny rail. Accessories attach by inserting “T-nuts” of an accessory through slots in the handguard and then tightening the bolts on the accessory. This rotates the T-nuts 90 degrees and locks the accessory firmly in place.

  • Advantages: Just like KeyMod, rails with M-LOK attachment are typically significantly lighter than 1913 Picatinny rails. As mentioned, M-LOK also fared better in head-to-head testing than KeyMod and is currently more popular, which means there are more choices and more quantities of accessories featuring M-LOK attachment. Another advantage of the M-LOK system is that it works well in polymer because of how the M-LOK platform was designed.
  • Disadvantages: Mounting accessories via M-LOK can be a bit tricky the first few times until you get a feel for it. Like with KeyMod, extra tools are required to mount M-LOK accessories—an Allen wrench, to be precise.

Three Daniel Defense Rail Systems to Consider


Daniel’s RIS II rail interface system was designed for USSOCOM for the SOPMOD II program. It utilizes 1913 Picatinny attachment and is a free-float design, so it doesn’t interfere with a barrel’s harmonics. Accessories can be attached at the 12, 9, 3, and 6 o’clock positions, and it attaches to a rifle via Daniel’s robust 6-Bolt Bolt-Up System. This is a classic rail system built for hardcore users sure to put it through its paces, using classic Picatinny attachment.

RIS II Rails from Daniel DefenseRIS II Rails from Daniel Defense

MFR Rail System:

This system utilizes M-LOK attachment, which helps reduce weight and also provides superior cooling properties. There are M-LOK attachment points located along 7 positions on the rail and an uninterrupted Picatinny rail along the top for attachment of an optic and other accessories that typically connect via Picatinny attachment. It attaches via Daniel’s Bolt-up System barrel nut. It’s a great choice if you’re looking for M-LOK and Picatinny attachment.

MFR Rails from Daniel DefenseMFR Rails from Daniel Defense


The brand-new RIS III rail interface system offers the tried-and-true toughness and durability of the RIS II but with M-LOK attachment for weight savings and the ability to attach accessories sporting M-LOK interfaces. You get the same proven free-float barrel design, durable aircraft-grade aluminum construction, and an uninterrupted upper rail platform with Mil-Spec 1913 rails of the RIS II—plus seven M-LOK attachment points along the handguard and integral QD swivel attachment points on both sides.

RIS III Rails from Daniel DefenseRIS III Rails from Daniel Defense

Other Factors

Once you’ve decided which type and style of rail is right for you, you’ll want to consider the following before making a purchase.

Rail Length

The maximum length of your rail will depend on the length of your rifle’s barrel, but you can certainly opt to go with a shorter rail and have mor barrel extend past its end. The length really depends on how many accessories you plan on attaching, how much added weight you’re willing to deal with, and personal preference.  

The Rail Manufacturer

No matter which style or type of rail you choose, you’re going to want to acquire it from a manufacturer with a reputation for quality. Unless you’re planning on putting a rail on your rifle and then just locking your rifle in a display case, chances are you’re going to put that rifle through its paces, and rails need to be able to handle it, stay attached to your rifle, and keep any accessories attached to them.

Make Sure the Rail Is In-Spec

This is a spin-off of selecting a quality manufacturer. It doesn’t matter which type or style of rail you choose if it wasn’t manufactured to exacting tolerances and is in-spec with the accessories designed to fit it. If it’s off even a bit, accessories will not fit properly and will not stay attached once they are subjected to recoil and any rough maneuvering of the rifle. So, avoid cheap knock-offs at all cost and go with brands known for quality—like Daniel Defense!  

Bottom Line

No matter which style of rail you choose for your firearm, you really can’t go wrong—unless you opt for a drop-in rail and it takes away from your rifle’s accuracy. So long as you choose a rail that’s manufactured by a reputable producer to tight tolerances, is in-spec, and built to last, it really comes down to personal preferences after that.

So, feel free to express yourself with your rail—and then with your accessories! It’s part of the fun of owning an AR15-style rifle!