AR-15 Fliers, Part 1

Most of us probably have some idea what constitutes a flier. I’ll give you my interpretation: "A flier is around that, without explanation, impacts outside the rest of the group." Closely related to fliers are fat groups and "walkers", two additional topics that we will give a little time to in this article. There are four causes of fliers that I am aware of. The first are marksmanship errors caused by the shooter. Second, sudden changes in range conditions that the shooter fails to notice.

Allow me to climb up on my soapbox for just a moment. Every long-distance shooter eventually gets caught by sudden changes in wind velocity or direction that occur on ranges. Masters and High Masters have cultivated skills that alert them to these changes but even these "walk on water" marksmen eventually get caught. So smart hombres use bullets with high ballistic coefficients at long distances to minimize the penalties of unexpected wind shifts. Third is gun and sight issues, Fourth is ammunition imperfections.

The first two causes are outside the purview of gunsmith fixes, though they’re important topics that can only be earned with plenty of quality live and dry practice. Eugene Stoner designed a fine rifle that has stood the test of time. The basic platform has been sold and copied in many foreign countries and has performed admirably in combat across the globe. Right from the factory, with no modifications, it shoots much better than it has any right to.

That being said, it was designed for reliability in combat, not super precise target shooting. There are certain features of its design that actually promote fliers. In the half century since its introduction, shooters, gunsmiths, and gun makers have recognized some of these shortfalls and compensated for them. Barrels and Tubes Let’s take a moment to look at those Stoner design characteristics that contribute to fliers and how they’ve been addressed.

First is attaching the forward sling swivel to the barrel via the front sight housing. Shooters using a sling to steady wobble and combat recoil can literally bend the barrel. This design issue intersects with marksmanship fundamentals. Those shooters who accept a lighter amount of sling tension than they would use with other firearms will likely experience less sling-induced fliers and their severity will probably be less. Regardless of the amount of sling tension applied, the consistency of tension is key.

This consistency not only applies from shot to shot but from one range session to the next. For example, if your last range session was in hot weather and your next trip was in cooler temperatures where you added a layer or two of clothing, that changes sling tension and your point of impact may well shift. A right-hand shooter applying a little more tension on one shot will probably experience a low left flier.

A float tube addresses this but can add a pound or more of weight so not everybody will want that solution. There are other options to lessen barrel flex from a supportive sling. Gun makers heard these early complaints about sling-induced fliers and zero shifts and reacted. Colt introduced the HBAR (Heavy Barrel). While using the same swivel, the fatter barrel lessens Center, handguards removed, exposing float tube. Bottom, this Geissele Automatics handguard also floats the barrel.

whip. When Service Rifle competitors began to seriously experiment with replacing the M14/M1A, demand for away to float AR barrels reached a fever pitch. Eventually, smart guys came up with float tubes. This is basically a pipe surrounding the barrel with a Delta assembly on one end and handguard endcap and sling swivel on the other. Thus, a tight sling can only bend the tube with no pressures applied to the barrel.

The float tube was sandwiched between the barrel and handguards, making it an internal modification and legal for Service Rifle. In the last few years both the National Rifle Association and Civilian Marksmanship Program have relaxed some of their rules for Service Rifle and Service Pistols. Rifles now permit AR handguards with rails on the outside, though there are some differences in NRA and CMP rulebooks.

Help your customer realize this and make them aware the onus is on them to comply with the rule(s) of the sports they participate. These various float tubes and modern handguards largely remove sling and other pressures from the barrel. This greatly reduces fliers but might induce other issues. One example, float tubes that throw the gas tube out of alignment with the Far key in the bolt carrier. Unfortunately, this is more common than a lot of folks realize and we will cover the problem in an upcoming section.

Carriers Another issue with Stoner’s design is the enormous amount of slop in the fit of the bolt carrier assembly inside the upper receiver. While that slop contributes to the incredible reliability of the AR, the downside is fat groups and fliers. Those precision issues are caused by the carrier not orienting itself so that the bolt face can be perpendicular to the center axis of the bore.

This, in turn, results in cartridges cocking at an angle inside the fat chambers found in most gas guns, especially those used by the military. A cartridge oriented at an angle in the chamber will send its bullet off center to the bore, deforming it and causing big groups and fliers. Function and precision in many gun designs are often at odds with one another.

As a gunsmith who custom builds ARs used at the highest levels of national competition and a former competitor myself with a half century of experience with this platform, it is my opinion that Stoner erred a little on the function side. That’s okay if you are going Far Top, a Les Baer, no longer available. Center, JP Enterprises. Bottom, Young Manufacturing, Inc. into combat in a dirty environment.

On the other hand, this article is about eliminating fliers so let’s see how we can do so by making accuracy improvements to carriers. Two companies have made part of this a little easier for us: JP Enterprises and Young Manufacturing, both of which offer National Match carriers with front ends that measure fatter than other carriers on the market. This results in more consistent positioning of the carrier.

When I was the match Armorer for the Army Reserve Shooting Team, I purchased 100 of these and tested the Team’s National Match Service Rifle uppers, first with stock carriers and then with match carriers. 100 is a nice sample size so I feel very confident in my results. The match carriers resulted in an average reduction in group size of 8.8%.

In all of my testing and then the hundreds of thousands of subsequent rounds fired by Team members in the uppers with the match carriers, I am not aware of a single malfunction caused by any of the match carriers. For more information on match bolt carriers, refer to my article in the May 2014 issue. Having improved the front of the carrier, let’s turn our attention to the back end. Shotgun an AR and note the gap at the back between the carrier inside the receiver. It is larger

at top and much smaller at bottom. This indicates that the carrier is not level and indicates tilt, which has been recognized as a contributor to fat groups. As the back of the carrier sags down, the bolt face cocks at an angle, causing a cartridge attached to the bolt to move out of alignment with the bore. Again, bullets are deformed and fliers and fat groups are common. Contemporaries of Stoner tried to fix this problem but were not successful.

Gunsmiths, with few exceptions, pretty much buried their collective heads in the sand for decades. I looked at what had been done nearly 50 years ago and the mistakes made and designed my own version of anti-tilt pads to level the carrier while not adding a bunch of friction. I drill and tap the back of the carrier at 4:30 and 7:30 O. C. to accept 5-40 dome head cap screws.

The small surfaces of the cap head that actually make contact with the bottom and sides of the insides of the receiver are only about the size of pin heads and offer minimum friction but plenty of support. This is covered in depth in the May 2017 issue. Testing revealed that anti-tilt pads cut group size an average of 14%.

When applied to a match carrier the two accuracy gains combined (8.8% plus 14%) and resulted in nearly a I had to mill a flat on this example to allow for proper gas tube clearance. quarter average reduction in group size along with fewer fliers. Gas Tubes A few paragraphs back I hinted at how gas tube alignment issues that arise with certain float tubes and handguards can work against keeping carriers level and centered on the barrel.

If there are any errors with the alignment of the gas tube and the bolt carrier key, the carrier will be pulled out of alignment, compromising any positive contributions of match carriers and anti-tilt pads. As Stoner designed his platform a person has to work pretty hard to create a gas tube alignment issue. Stoner’s design allowed the gas tube to float from the rear of the front sight all the way into the cloverleaf hole in the front of the receiver.

When smart guys invented float tubes, they inadvertently opened a can of worms. Float tubes take up considerable room under the handguards and sometimes that brings them into contact with the gas tube, pushing on it and forcing misalignment. Holding an upper with a float tube to light needs to show a line of white between both tubes. If it doesn’t, the contact will cause problems. My March 2014 details how to fix this. Most of these problems occur when the float tube is 1 3/8" in diameter.

Compass Lake Engineering manufacturers a skinnier tube at 1 1/4" that they supply with a properly-bent gas tube and outer plastic handguards designed to give proper clearances. This CLE model is highly recommended. There has been a recent trend to replace regular A2 plastic handguards with rigid handguards that have rails outside. While these new units may float their barrels, some are ill designed.

What they are using to replace standard barrel nuts are often too fat and push up against the gas tube so that the tube enters the cloverleaf at an upward angle. When the bolt carrier key goes over such a cocked gas tube the whole carrier is forced upward at an angle. My May 2018 article discusses this. When a customer hands me an upper complaining of fliers, I look at two things first: Ammunition issues and gas tube alignment. It’s that important!

Chambers The 5.56mm NATO chamber is the correct choice for soldiers going into the dirty conditions of combat. For the rest of us, a number of its characteristics just contribute to fliers and fat groups. The NATO chamber has an overly-long freebore that bullets must pass through before reaching the back of the barrel. Complicating matters is the fatness of the freebore which exceeds that of other chambers, making it easier for bullets to begin to tip.

Barrels that begin life with long fat freebores will "wear out" sooner. If you gunsmiths take in a rifle with a NATO chamber from a customer who is complaining of fliers, be sure to ask if this has just started or if it has been a problem from the get go. If fliers have been common, even when the barrel was new, this may point to a rifle that needs anew barrel. If fliers began around round count 2,000 that barrel may have reached its wear out point.

I recommend using something like the Hornady Overall Length Gauge or the newer Dead Center Sports Length To Lands Gauge to take a measurement with the same bullet that the customer is shooting. As a general rule, when bullets are jumping 1/4" or more, fliers are becom-

ing more common, more severe, and groups are opening up. Such barrels may need to be replaced. If you are replacing a barrel or performing anew build for a customer there are three chambers that I can recommend. The Compass Lake Engineering chamber is great for customers who want to shoot nothing but magazine-fed ammo, including issue ball ammo. For shooters using magazine-length ammo at short distance and then switching to longseated bullets for longer distances, this is a great chamber.

The Wylde chamber has a longer freebore than the CLE. Like the CLE chamber, it will perform well with any magazine-length rounds. For folks wanting to switch to long-seated bullets in heavier weights (90 grains for 5.56/223) this is my choice. As of this writing, the Wylde chamber is very popular. The final recommendation is a very limited specialty chamber, the 223 Remington Kiff ISSF chamber available from Pacific Tool & Gauge. This has a very long freebore, about 1/10" longer than a Wylde.

It was developed by Dave Kiff, the owner of PT&G, for shooting 90 and 95 grain bullets fed one at a time by hand into the chamber. Due to the extremely long freebore it should not be used with magazine-length ammo because bullets will be jumping too far. It is a good The proper way to square AR receivers is in a lathe. Using one of the so called "AR lapping tools" pictured here will normally make receiver run out worse, not better. chamber for long range matches like PALMA and F Class.

Receiver and Barrel The fourth design failure of most all Stoner firearms is the sloppy fit between the barrel extension and the inside surface of the upper receiver. When assembled, the barrel nut does an adequate job of preventing front to rear movement of the extension inside the receiver. Unfortunately, however, a lot of up and down and left to right movement is possible.

The Army Reserve Shooting Team discovered this issue over a quarter century ago while in Australia, which I detailed in the March and April 2013 issues. Gunsmiths need to tighten up the extension-to-receiver fit by using either shim stock and green Loctite or oversized BAT Machine match extensions. Properly done, you can expect about a 1/3 reduction in group size and a reduction in fliers. Heavy sling tension applied directly to barrels bends the barrel.

Those same sling pressures can also cause the extension to move inside the receiver. Keeping that extension centered in the receiver lessens the negative impacts of sling pressure. Eliminating movement of the barrel extension inside the upper receiver relates to the "registration point", the position of the muzzle from shot to shot. Failing to have a consistent registration point allows the barrel to go through its harmonic whip upon firing but the muzzle doesn’t return to its previous point.

This is what happens when you have a lot of slop in the fit of the barrel extension as movements at the back of the barrel are translated to movements at the muzzle. This inconsistency is also influenced by the front surface of the receiver. Almost all of these receivers come from the factory with high spots on the fronts where the raised portion of the barrel extension comes to rest when the firearm is assembled. Those high spots allow the barrel to pivot around during the harmonic whip.

The muzzle on such a firearm is guaranteed not to return to the same point between shots. The front ends of most all receivers will need to be properly squared. Make no mistake that so called, "Upper Receiver Lapping Tools" that sell for about $35 from a number of sources is not the proper way to accomplish this task! These tools fit in a 3/8" hand drill. My tests show that runout actually increases from the use of these gizmos.

We want runout to decrease and the way to accomplish this is by proper machining on a lathe. When this is done properly average group size will decrease by a substantial 14%. Finishing up this section with the fifth and final design flaw in Stoner platform rifles is upper to lower receiver fit. As we all know AR lowers attach uppers by way of two captive push pins. While this is indisputably convenient it sure doesn’t contribute to precision.

My April 2017 article on the Accu- Wedge details a 26% reduction in group sizes in one of my lowers by simply dropping in this piece. Some high points are that each upper/lower combination will exhibit its own specific group reduction, that every AR has two pins and tightening at both is key, and one of the best solutions is to start your build with a tightly matched receiver set such as available from Rock River. Next month we will get into fliers caused by ammunition characteristics.

Feel free to email me at to discuss this or any of the articles I’ve written. AG