The AR15 platform has evolved so much over the past 20 years, so as types of rail systems for AR-15 besides the plastic two piece handguard.
The add modularity and mounting space to improve the AR15's handling and capabilities. Drop in and free float rail handguards are the most popular.
Types Of Rail Systems For AR-15
Drop In
Drop in rail systems use special points called Picatinny to attach things. One popular style is the quad rail, which has four rails going all the way. However, full length quad rails can get heavy as the length increases
Free Float
Free float rail systems are usually made of aluminum, not Polymer. They're known for better shooting accuracy. That's because they don't touch the rifle's barrel, letting the barrel flex more freely to preserve barrel harmonics. This small change can make shots more precise. Imagine putting weight on a long stick; the stick might bend a little.
Rail Mounting System
M LOK
M-Lok is the go-to method for attaching stuff to an AR-15 rail system. Magpul created M-Lok, which means "Modular Lock." Any company can get permission from Magpul to use this design, making sure all M-Lok items have the same quality.
To use it, slide the t-shaped nut into the slot, turn it until it's tight, and it locks in place. Recent data from USSOCOM proves that the M-Lok system is great at handling bumps and hits. This means your accessories will be safe and secure using M-Lok.
KeyMod
KeyMod is a popular way to attach things to AR-15 Rail systems and handguards. You can spot it by its keyhole-shaped slots. To use it, push the accessory's lug through the wide part of the slot. Then, slide it to the narrow part and tighten with an allen screw.
The design helps attachments line up on their own. While many like the KeyMod system for the AR-15 rail, the M-Lok system has more support.
M1913 Picatinny
Picatinny rails are found on many guns, not just the AR-15. The Picatinny Arsenal in New Jersey gave them their name. They made this rail in 1995, inspired by the Weaver mount.
All Picatinny rails have the same size. These rails look like metal strips with a T-shape and flat spots. Some are milspec and some are not. This design lets you slide on accessories and lock them tight. Each rail usually has numbers, so you can put optics in the same spot every time. Most modern AR-15 guns have these rails.
M1913 rail sectional pieces can also go on M LOK and KeyMod handguard systems.
Rail System Lengths
Popular AR-15 rail system lengths include:
7-9 inches: Suitable for carbine-length gas systems and often used for close-quarters applications. It still offers enough rail space to mount grips, light and additional niche accessories such as sling attachment points.
12-15 inches: This length covers mid-length and rifle-length gas systems, providing a more extended C grip, better accessory space, and increased accuracy potential at longer ranges due to the longer sight radius when using iron sights.
16 inches and longer: These are often used for to increased accessory space and longer sight radius if using iron sights. It also provide tripod mounting point that is further away from the main receiver to provide stability. A long rail can also cover up the barrel so a hot barrel doesn't burn the user when carrying the rifle on a sling.
Main Takeaways
Versatility: Different lengths serve diverse tactical needs. Shorter lengths provide more agility in close quarters only when paired with shorter barrels, while longer lengths provide stability for precise shots at distance.
Accessory Mounting: Depending on the user's requirements, the rail length determines how many accessories, like lights, lasers, grips, and sights, can be mounted.
Weight and Balance: A longer rail adds weight to the rifle but can also balance out a rifle with a longer barrel, affecting the overall feel and handling of the firearm.
Aesthetic: Some users prefer the look of a longer rail that covers most of the barrel, offering a streamlined appearance.