Firearm Rail System Differences, Explained

If you’re relatively new to the wonderful world of firearms, you may not understand the differences between Arca Swiss and Picatinny rail systems.

Both systems enable owners to mount accessories on their firearms, but there are a few subtle differences that we’ll briefly explain below:

Arca Swiss

Arca Swiss systems have existed in the United States since the 1960s, but they weren’t popularized in the firearms industry until the 1990s.

First used in the cinematic industry, Arca Swiss utilizes a two-piece locking mechanism to quickly attach and release a camera, lens or other accessory to your firearm or tripod.

The first piece of the mechanism is a plate (standard 35mm). This plate attaches directly to your accessory with a standard ¼-20 screw. Certain accessories or plates may be necessary for specific models.

Kopfjäger Reaper Rail System - Arca Swiss

The second piece of the Arca Swiss system is the mounting base, which clamps securely to your firearm or tripod. The plate might simply be the physical connection between your firearm and tripod.

The clamp on the mounting base can be completely opened, enabling the Arca Swiss plate to slide into position and continue to operate.

In a sense, Arca Swiss is the glue that holds your firearm-tripod or camera system together. Its biggest advantage is the rapid mounting and dismounting, allowing equipment to be quickly changed out or adjusted without fears of anything coming detached.

There are other components to most Arca Swiss systems, depending on your purchase. Modular brackets, L-Brackets, lens feet, collars and additional clamping systems might be necessary, depending on your setup.

A quick-release Arca Swiss mount for cameras

Before you ever purchase an Arca Swiss system, be sure to consult with experts to ensure that your accessories will be compatible.

Generally, Arca Swiss systems are used for professional photography arrangements. With the mobile plates and various clamps, the different Arca Swiss configurations are virtually unlimited.

Perhaps the most useful aspect of Arca Swiss is the standard plate, which is almost universally compatible with other Arca Swiss systems.

Picatinny

The Picatinny rail system is more well-known than Arca Swiss. Sometimes called a 'Pic rail', the Picatinny's purpose is clear – to act as a standard rail interface system to mount firearm accessories. This includes iron sights, scopes, tactical lights, lasers, foregrips, bipods and more.

Picatinny rails were standardized for the US military circa 1995 to attach to M16s and M4s. Since then, Picatinny rails have become the pre-eminent rail system across the world to affix accessories to firearms, usually ARs. 

A Picatinny Rail

A Picatinny rail can be affixed to either the top, bottom or side of a standard rifle barrel. Certain, smaller Picatinny's can also be used for pistols, crossbows, paintball and airsoft barrels. 

The basic design of a Picatinny rail is a straight, flattened metal piece with crosswise slots at equal intervals along the rail. These slots are where accessories are secured and locked into place.

Other Rail Systems

Picatinny has a cousin, the Weaver Rail. Weaver Rails are a light rail system, very similar to Picatinny, in fact. Almost any accessory that fits on a Weaver Rail will also fit on a Picatinny, though the opposite isn’t always necessarily true.

A Weaver Rail

Two more popular systems are the KeyMod and MLOK systems, which enable the attachment of accessories without the needs for adapters, as long as the user aligns the lugs and keyholes on the rail first.

The great appeal of KeyMod and MLOK systems is their ability to 'lock' accessories into place via specially-cut slots in the rails, so users never need to worry about anything becoming disconnected. 

A KeyMod Rail

KeyMod and MLOK systems are usually lighter than Picatinny rails, due to not requiring an adapter for most accessories.

However, in an effort to become a universal adapter, KeyMod is often blamed for not allowing accessories to mount correctly because the pre-cut slots weren't accounted for beforehand.

An MLOK Rail

Essentially, KeyMod and MLOK are pre-cut rails to attach certain, specific accessories to rails. Their pros and cons, as related to Picatinny rails, are entirely user and purpose-specific.

There is another rail adapter system known as 'Arcatinny'. This is a combination of Arca Swiss and Picatinny rails that has features of each. An Arcatinny might be excellent if you're hunting and recording your harvests, or if you're simply observing wildlife but want to retain the ability to take photographs and videos.  

An Arcatinny Mount Adapter

Which Rail System is Best?

This question is not easily answered. Before you purchase a rail system, you should always consider your purpose.

Are you hunting? Which accessories are you using? Are you just taking pictures or observing wildlife? For cameras, Arca Swiss is the go-to locking system onto tripods.

For rifles, Picatinny is generally the rail system of choice to affix accessories.

This article is not exhaustive. There are numerous rail nuances and personal preferences that should be considered before committing to a rail system.

The most important factors when considering rail systems are ease of use, convenience, weight, and of course, purpose. The only 'right' way to use a rail system is through the method that achieves your goals.