Rifle Attachment Systems Old and New

Use of precision, long-range, bolt-action rifles has increased dramatically over the past few years. Let's look at some of the attachment systems also used on MSRs and other popular gas-operated firearms.

Rifle Attachment Systems Old and New

Use of precision, long-range, bolt-action rifles has increased dramatically over the past few years. Let's look at some of the attachment systems also used on MSRs and other popular gas-operated firearms. (Photo: Alan Clemons)

Use of precision, long-range, bolt-action rifles has increased dramatically over the past few years. No longer just hunting, F-class or sniper rifles — they have taken on new roles. Along with this expansion, the use of accessories integrated into the rifle has become the norm. Understandably, some of the attachment systems used to interface these accessories to the firearm are also used on MSRs and other popular gas-operated firearms.

Initially, many firearms had dovetails machined or mounted into the top of the receiver to accept a telescopic sight. However, what we would consider the oldest of the systems currently in use, the Weaver mount, was created by William Ralph Weaver and designed to mount optics to rifles. It is noted for being mounted solely above a receiver and having rounded slots.

In the mid-1990s, the U.S. military adapted the Weaver rail and created the MIL-STD-1913, or Picatinny, rail. You may also see it referred to as a Pic rail. It was created by averaging the dimensions of 20 different Weaver rails taken from the inventory at New Jersey’s Picatinny Arsenal and adapting them to a scaled down version of a rail used on the 105mm howitzer to facilitate production and inspection specifications. The Picatinny standard is much more angular than its Weaver predecessor.

This is the standard across the U.S. Department of Defense and has also been adopted by NATO (STANAG 2324) and other international militaries.

Picatinny rails are often indexed with markings that allow the user to quickly ascertain where on a rail an accessory should be mounted. These markings are in the recoil grooves that are continuous down the length of the rail, whereas on a Weaver rail, there may only be a few of these.

Both Weaver and Picatinny allow the mounting of rail grabber-style accessories. There are a multitude of different mechanisms available and may be quick-attach with a lever actuator or what is considered permanent mount with a screw tightener. The former can be accomplished without tools, but the latter requires a wrench and the device is then often cemented into place with Loctite on the tension adjustment nut.

For years, the military mounted continuous Picatinny rails to firearms to attach accessories, which had grown in number from telescopic optics to include iron sights, tactical lights, laser aiming modules, night vision devices, reflex sights, foregrips, bipods and slings. Today, many of these will also be used with precision rifles.

Although it’s now a footnote in history, in the early 2000s the Heckler & Koch XM8 Rifle introduced small oval holes in the handguard to attach accessories called Picatinny Combat Attachment Points. PCAP was touted as “negative weight” because it removed material rather than mounting yet another continuous rail. Despite the name, PCAP was not Picatinny rail-compatible without an adapter that fit into the ovals and stayed in place with spring-loaded pressure.

Although impractical, PCAP got others to thinking about ways to place attachment points only where they were needed. That led initially to the KeyMod system, developed by Eric Kincel of VLTOR firearms and initially offered on Noveske rifles. The name is a portmanteau of “Mod” meaning modular, and “Key” referring to the key-hole profile of the mounting slots. Into the slots are inserted bolts with nuts on the end. The bolts are tightened and the mount grips the material of the platform to stay in place.

Heckler & Koch has a similar system it refers to as HKey and is often referred to as HKeyMod. 

Interestingly, the U.S. Army’s new Compact Semi Auto Sniper System is made by H&K, but the Army directed H&K to swap its proprietary system for M-LOK standard.

Not long after KeyMod hit the market in 2012, Magpul Industries unveiled its Modular Lock system, M-LOK. It is an improvement over Magpul’s MOE attachment, which was created in 2007. It relies on standard sized cuts in the platform that,like KeyMod, accept accessories that are held fast with tightened bolts.

The advantage of all three is these systems is that they allow for lower profile rails and the shooter can mount accessories only where they are needed.

While KeyMod is open source, M-LOK is not. Magpul doesn’t charge a license fee, it doesn’t get to decide who can use it. Despite that, it has surpassed KeyMod in popularity. Not only that, but a test by the Department of Defense found that M-LOK was a stronger and more reliable attachment. Although limited in scope, the military has slowly begun to adopt its use, but only in conjunction with Picatinny rail adapter sections rather than M-LOK accessories.

For years, precision shooters used Manfrotto ball mounts and tripods, often times with homemade adapters. Unfortunately, the weight of a precision rifle complete with optics and perhaps other accessories can be a bit too much for the Manfrotto design, which is intended for use with cameras. Naturally, shooters liked the lightweight of the Manfrotto, but looked for something more robust.

The new hotness for precision firearms is the introduction of the ARCA or ARCA-Swiss and Really Right Stuff Quick Release standards. These come from the camera industry and have been adopted in order to facilitate the attachment of firearms to tripods. These are mounted to the bottom of a stock or rifle chassis, although some manufacturers are leveraging the lightweight architecture to mount select items to the sides of the firearm as well.


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