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Knight's Rail Interface Systems
Rail interface systems have been all the rage since Knight's won the first military contract for the SOPMOD M4 a few years ago. It was around 1999 when these overpriced supergizmo hand guards hit the tactical parts market and being into some money, I decided to pick up a set for one of my ARs. That was during a period of price inflation hysteria in California, where it actually made sense for a while to spend $300 on a set of hand guards when some people were spending $3000+ on guns that had only cost maybe $1200 a few months before. The big pull of these hand guards, other than being genuine USSOCOM issue, was that once you have a set of the hand guards on your rifle that have the standardized rail interface, you could then open up options of standardized accessories that would never be made to fit specific guns, but rather the standardized rail interface system. Once the standardized rail system dimensions are set, diverse accessory makers can simplify their manufacturing to make accessories adaptable to the rail, therefore adaptable to a more diverse number of weapons without needing to produce specialized models to suit individual weapon product lines. Thus, the initial investment in the rail system is recovered in a generally lower cost and better fit of the various compatible accessories. It also helps to avoid some of the patent and copyright issues that have been a source of manufacturer squabbling in the past.
That whole rail system is where the folks at Knight's and the US Army Natick labs got together to come up with a systems approach for small arms accessories that were multiplying like rabbits. Back in the day, a troop might have an optic attached to his rifle, maybe an issue M203, and beyond that was the issue bayonet. It was pretty racy and high speed for a soldier or Marine to use green duck tape (also known as 90Mph tape) to attach a flashlight to the hand guards of his rifle. In all reality, all of this was pretty uncommon, and it was not unusual for troops like myself to be threatened with charges if we mounted a privately purchased scope on an issue rifle. The SOPMOD and new thinking among infantry experts changed that. The idea being is that if something helps to complete the mission, it is worth trying. Probably the most sought after and simplest improvements are vertical grips added to the front of rifles. These greatly enhance handling characteristics of the weapons in environments where the shooters must constantly contort and shift shooting positions to meet the situation.
Nowdays, most commanders allow and encourage the use of the rail system for mounting these accessories to various weapons. The SOCOM mods were all modular, and included such accessories as a foregrip, both visible and IR lasers, flashlights, a few different types of sights, grip panels, a grenade launcher, and even a thermal sensor. The beauty of it all is that you can put a rail interface on otherwise very different weapons and the accessories will then become compatible. This idea is actually not very high tech and could have been done a long time ago, but ended up taking his long to incorporate into small arms upgrades. Custom armorer are even retrofitting rail interface systems to very old weapons like the M14, G3, FAL, and Uzi. Even the old MAG-58 which is a derivative of the 1930s Bren gun gets a compliment of rails for mounting such items as optics, PAQ-4 and PEQ-2 lasers, and most likely in the future, an improved bipod.
The Knight's Rails made by Knight's Industries of Vero Beach FL are probably the highest quality rail systems on the market. They also have rail handguard systems for a more diverse selection of weapons than any other maker, although a number of clones and competitors have their own rail systems. The Night's handguards tend to be the most costly of the bunch, but they offer the most features. Knight's handguards have threaded holes in every five slots, and most of them have the slots numbered with an "address" for assisting in standardized placement of accessories on different weapons. Almost none of the clones have these features. The RIS for the HK93 shown here is a Genuine Knight's item (no clones have ever been made for it due to low demand) but lacks the "address" markings on the rails. All of the genuine and replica handguards use the same basic grip panel design. The grip panels do come in several lengths, but users usually get the standard length panels (three are included with each RIS/RAS) and cut them to length so that they fill in spaces between accessories. Note, that on longer RIS units, you end up with a lot of uncovered space because the panels are only about half as long as the rails. The panels are sized to match the M4 length handguards. Mounting varies according to the weapon, but in all cases, it is geared toward making the rails as rigid as possible without adding too much weight to the weapon or interfering with function. This means a much tighter fit and more exacting tolerances than factory original handguards. In the case of the HK rifles and submachineguns, that means the use of a bolt and locknut to secure the front of the handguard instead of the original pin. The "ears" that interface the aluminum rails with the rest of the gun are made of stout heat treated steel. Original HK handguards are simple aluminum lined plastic, and even the mounting holes are not particularly tight. This meant that original HK bipods tend to wiggle and rattle, not so with the Knight's upgrade.
Freefloat variants of the handguards are probably the most commonly copied type. These are favored by civilian shooters because freefloat handguards give better accuracy because of less interference with the barrel. Only some fairly rare and specialized versions of military issue rifles actually use the freefloat handguards. The Crane labs Special Purpose Rifle is used only by some Special Operations units as a designated marksman's rifle in situations where they determine that the mission is best served without the use of a traditional sniper rifle. The SPR is basically a highly accurized M16A4 and will often come with a sound suppressor. The retrofit M4 type handguards, although good, are not usually as firmly secure as the freefloat types and therefore not quite as good for precision sights. Still, the retrofit M4 RIS design is one of the most popular because it is relatively easy to install and compatible with the M203 grenade launcher.
For just about anyone who is not a government contractor or actual special operations operator, the clone handguard has all of the most important features and accessory compatibility. Be warned, there are some dealers out there who are simply repackaging the clone accessories as the more costly items from Knight's GG&G, and ARMS. Quality on the replicas can be so good that it is little more than an issue of honesty in pricing, but still, it is an issue to watch out for when shopping.
Some of the better clones come from the Airsoft accessory makers, but there are subtle differences in some critical dimensions that require adaptation for them to work on "live" weapons. In some models, like those made for the Mp5, a few of the Airsoft Mp5, the require modifications are extensive and not very cost effective. Most of the clones use 60 series aluminum castings while the Knights handguards use 70 series machined forgings.
Still the clones are very functional, and will accept nearly all of the standardized accessories. There is no particular patent on the actual rail dimensions, so the various manufacturers do usually get them right. The only people who seem to have a real problem producing anything with compatible rails are in the former Soviet countries, where their engineers insist on using oddball proprietary rail dimensions or obsolete "Weaver" rail dimensions which are actually different from the M1913 Picatinny arsenal standard that was accepted for the "flattop" M16 and M4 rifles.
Custom built AR type rifles utilizing rail handguard systems take advantage of enough modern innovation that the owner often has nothing left to desire in getting a "preban" configuration. Combining rail handguards with one of the newer stocks like the Ace ARFX stock shown here gives a truly modern rifle. One irritating note on this one, however, has been the muzzle brake which produces a fairly pronounced fireball of a flash signature that is visible through the scope. Note how three scope rings are used to secure the scope to the rifle, two on the receiver and one on the handguard. This allows for optimal placement of the rear lens of the scope and eye relief to match the ergonomically correct original location of the M16 rear sight. The adjustable bipod and foregrip are moderately priced, and if the user wishes to reconfigure the rifle, these accessories can be removed with minimal effort. Mounting a 1" diameter flashlight liek the Tac-Star or Surefire on the handguard is very easy with the use of some spare standard scope rings. Likewise, advanced items like lasers, both visible and IR can easily find a place on the handguards on an as needed basis.