Presentation, Feed, Consumption: The Auto-loading Cycle

Think of it like dinner at a restaurant. The chef prepares your food and arranges it on the serving plate to be attractive. The server carefully places your plate on the table in front of you and adjusts it so the presentation is precisely aligned with your sight picture. You now dig in, forking chewable portions into your mouth for consumption. A similar sequential process takes place in auto-loading firearms. A loaded magazine presents the cartridge at precisely the right height and angle for the bolt/slide to carry it forward into the firing chamber. You pull the trigger, the spent (consumed) cartridge is extracted, and the loading cycle repeats itself. What can possibly go wrong with something that simple?

The magazine’s presentation of the cartridge is the first critical step in all auto-loading firearms’ operating cycle, and it is a key element of firing reliability. Whether the magazine is detachable or internal, it must present the cartridge at precisely the right height and angle to the bolt/slide’s forward loading stroke. This is achieved by an internal magazine spring that is attached to the magazine’s footplate (located at the magazine’s bottom end) and a follower that rides on the top of the spring, which both lifts the rounds and holds them under spring tension against the magazine’s feed lips (on the magazine’s open end) in presentation position.

When loading the magazine, the cartridges are pressed into the magazine’s open end, one on top of the other, or in tubular magazines—one behind the other, which compress the magazine spring. The follower rides on top of the compressed spring at the base of the cartridge stack. Its purpose is to power the stack upward by spring decompression during the weapon firing cycle and present each round at precisely the right height and angle to be fed into the firing chamber.

The clear majority of feed malfunctions are directly related to improper magazine-cartridge presentation. This is to say that feed malfunctions often result when the cartridge is presented either too high, too low or at the wrong angle to be properly met by the bolt/slide and carried forward into the firing chamber. There are several root causes that all involve the magazine. Here’s what to look for.

Cartridge presentation is a critical element of feed reliability. A stripped 1911 Government Model with a loaded magazine inserted in the magazine well demonstrates the proper installed height and cartridge presentation.

Root Causes of Malfunction

Load a magazine to its advertised capacity. Observe the angle at which the top round is presented. Now, carefully unload it, one round at a time. Compare the presentation of every following round for presentation consistency. Every round should look the same. If the rounds begin to change presentation angle as the magazine empties, you may well have either a follower-drag issue or a weak spring issue. Both are replaceable. However, if the round being presented appears loosely held in place by the magazine feed lips, or shifts easily beneath the feed lips as the magazine empties, the presentation problem may well be the feed lips themselves.

Feed lips wear out over thousands of rounds, and they can easily become bent by dropping your magazines on a hard surface or stepping on them. Don’t bother trying to readjust the feed lip angles by bending them back into what looks right, because it never will be—unless you happen to get lucky. Discard magazines that have damaged or worn feed lips. Don’t save them for range use—get them out of your shooting life permanently.

A magazine’s installed height is another malfunction culprit. A magazine that is installed too high will drag on the bottom of the bolt/slide. The telltale sign is obvious wear on the top edges of the magazine’s feed lips and wear marks on the bottom of the bolt/bolt carrier/slide where it passes over the magazine feed lips. What causes this condition?

Most modern magazine designs have a magazine stop in some form that visibly protrudes from the magazine’s body. In most pistol magazines, the magazine base plate acts as the stop. The stop makes positive contact with the gun’s magazine well, limiting the depth the magazine can be inserted. The purpose of the stop is to prevent over-insertion into the magazine well from a reloading palm-slap or careless grounding of the installed magazine on a hard surface.

This condition can also result from excessive wear on the gun’s magazine catch or the magazine’s catch hole that holds the magazine in place at the specified height. High capacity magazines weigh considerably more than factory-spec magazines. Loaded high capacity magazines put much more sheer stress and wear on the magazine well catch and the magazine’s catch hole. This wear is easily detectable by a loose-fitting or “sloppy” magazine. In this case the bolt’s forward stroke either misses the cartridge altogether because the cartridge presentation isn’t high enough, or it only contacts the cartridge partially, driving it downward and away from the firing chamber. Again, jam city.

In all cases, when a magazine is out of spec, replace it with a new factory magazine. Aftermarket magazines may appear to be exact clones of factory magazines, but they’re usually not unless you purchase pricier competition magazines offered by high-end manufacturers. Again—don’t keep magazines that chronically malfunction. Don’t save them for range use or give them to a less experienced shooting friend. Throw them away.

During the auto-loading feed process, cartridge travel is another critical reliability factor. Let’s imagine the cartridge traveling toward the firing chamber as it leaves the magazine. There should be no point during this travel where the cartridge isn’t either held by the magazine feed lips, or partially chambered on the bullet nose-end while being grasped on the cartridge casing’s bottom-end flange by the bolt face and/or extractor. Securing the cartridge during its travel forward from the magazine into the firing chamber is critical so that the cartridge doesn’t fall out of the gun while the bolt/slide is on its forward stroke. It also ensures feed reliability no matter what angle the gun is being held, e.g., vertically up or down, upside down, etc. Hollywood depicts weird gun holds because they look cool on screen, but there are times in extremis when one may need to reliably fire and cycle in all those positions.

This brings us to the feed ramp and its purpose. Most breech loading, magazine-fed automatic, semiautomatic and some manually operated firearms are equipped with feed ramps. Feed ramps are easily identifiable because they’re usually a tightly machined and polished metal ogive-shaped ramp located on the outside bottom of the gun’s firing chamber. The feed ramp’s sole purpose is to reliably guide the cartridge into the firing chamber as it leaves the magazine on its travel forward.

Comparing a number of different auto-loading firearms reveals there are several different feed ramp designs. For example, the AR-7’s feed ramp is part of the magazine; on the Mauser C96 it’s part of the receiver; on many pistols the feed ramp is part of the barrel. Some designs are even more subtle, like FN’s Five-SeveN pistol, which incorporates a beveled firing chamber that acts like a feed ramp.

Feed ramp geometry and cleanliness is critical to the firearm’s proper reloading cycle, making it a common point of mechanical failure. If you’ve been experiencing jams (especially when shooting one or two different shaped bullets) and you’ve already done the troubleshooting on your magazines, it’s prudent to check out the feed ramp. Here’s what to look for.

A variety of loaded magazines demonstrating different brass, steel, aluminum-cased ammunition. All have different design installed heights and presentations to the bolt/slide forward stroke.

Check Out the Feed Ramps

Feed ramps should be smooth and clean. That said, it is not uncommon to see copper deposits on the feed ramp or manufacturing milling marks. Not all manufacturers polish their feed ramps. However, if you detect an obvious rough or deformed surface, rust, pitting or the presence of attached debris (metal, carbon, grit, etc.) on the feed ramp, you can bet on the fact that the bullet nose is likely being directed off-center as it is fed forward into the firing chamber. This will almost always cause a failure to feed at some point during the forward loading stroke. The solution most shooters immediately turn to is polishing the feed ramp. While that may or may not be the solution to your failure-to-feed problem, have it done by a seasoned professional gunsmith; attempting it yourself is a bad idea, and here’s why.

Don’t Polish the Feed Ramp—Seek Professional Help

There are a number of critical, yet subtle, geometries in play when polishing a feed ramp, and changing any of them, even slightly, can cause physical damage, further exasperating the malfunction. It is important to understand that the associated tolerances involving the angles (geometry) of the gun’s frame, feed ramp and barrel throat are critical. For example, polishing the feed ramp risks rounding (radiusing) its top shoulder. Radiusing changes the shoulder angle and redirects the bullet nose off its design course of alignment into the firing chamber. The result—back in jam city. Plus, the damage you create from do-it-yourself polishing, will ultimately require an expensive professional fix.

Presentation comparison between new 1911 Wilson Combat and worn 1911 MILSPEC issue .45ACP magazines. There are about 3 degrees of difference in cartridge presentation angle between the new (foreground) and old (rear) magazines. Using the old magazine is asking for a jam.

Shape and Velocity

There are two additional variables that influence feed reliability. They are the shape of the bullet nose and the velocity of the ammunition you’re firing. As a general rule of thumb, a rounded bullet nose feeds more reliably than a pointed bullet nose, because a pointed bullet is less forgiving to feed ramp angle fluctuations and frame gaps during the feed process. Hollow points and flat-shaped bullet noses with sharp shoulders often wobble up the feed ramp, especially at higher bolt/slide velocities contributing to feed malfunctions.

Second, using ammunition that provides above-average (higher) bullet velocities means a hotter load is being used to propel it. That translates to higher bolt/slide stroke velocities (cyclic rate). When the bolt/slide cycles at higher velocities, it is more sensitive to “tight” magazines that are slower to feed. The resulting mismatch almost always leads to jam city.

If taken individually, none of the variables discussed above may cause a feed malfunction, but their cumulative effect almost always will. It is for this reason that several top professional gunsmiths offer a “Reliability Package.” As part of this package they hand-lap all frame, slide, barrel bushing, BCG, etc., and wear points for perfect fit. They polish the feed ramp to a radius that best matches the ammunition you tell them you primarily shoot. And they’ll adjust all the magazines you provide them (or purchase from them) for installed height and perfect cartridge presentation. The result is a “tuned” firearm that is as close to 100% reliable as can be mechanically attained, and it’s worth every penny if you’re betting your life on it.

Consumption

The final step in the process is consumption—firing the chambered round. Many never consider the dynamics involved when the gun goes bang and the cyclic operation that immediately follows. So let’s step through the consumption (firing) sequence and take a look at the dynamics.

Once a live round is chambered and the bolt/slide is closed and locked (in battery), the gun is ready to fire. When you pull the trigger either a hammer or a striker hits the cartridge primer. The primer fires and ignites the propellant. The propellant burns at its predetermined velocity, producing extremely hot, rapidly expanding gases as a product of propellant combustion. As the gas expands it “swells” the brass case against the firing chamber. At the same instant, it propels the bullet from its seat in the neck of the cartridge case forward onto the lands (spiral groves) running the length of the barrel’s bore. The exceptions are smoothbore shotguns and muskets, which don’t have lands.

The round has fired. As the gas continues to expand, the bullet increases velocity and spin inside the bore. The spin acts to gyro-stabilize the bullet inflight. As a bullet leaves the gun’s muzzle it becomes a ballistic projectile and subject to gravity and drag. It has achieved all the velocity it can attain. It can go no faster, and from this point on it will only slow down from effects of aerodynamic drag.

At the same moment the cartridge fires, the backstroke process begins. It’s a process because depending on the operating system’s design there may be a few milliseconds’ delay designed into the backstroke sequence. Regardless, the bolt/slide now begins its backstroke.

The backstroke accomplishes several purposes in addition to extracting the spent cartridge case from the firing chamber. As the spent cartridge fully clears the firing chamber, it contacts an ejector (usually positioned along the side of the lower receiver or lower frame). During the rearward travel, the base (primer end) of the spent cartridge contacts the ejector, and the case goes flying from the open ejection port of the gun.

The backstroke continues compressing either a recoil spring or buffer spring, which accomplishes two essential elements. Spring compression slows and stops the rear stroke, and the compressed spring stores the energy necessary to reverse the bolt/slide’s direction forward with the proper velocity to achieve the loading cycle previously discussed. At this point we have examined the complete presentation, feed and consumption cycle.

Feed ramps come in different forms depending upon the gun’s design and feed mechanism. Pictured is a stripped 1911 Government Model with barrel in place and loaded magazine installed. Note the polished feed ramp at the bottom end of the barrel. Even slightly changing the ogive geometry will cause jams.

It’s Complicated

As you may now understand, the process is a complicated sequence of mechanical steps exacted upon proper machine tolerances and regular maintenance. It is solely powered by the pressures resulting from propellant combustion, which also has a design-operating envelope. As such, there are many critical operating elements that can go wrong and cause a feed or extraction malfunction. Hopefully, you now know where to start troubleshooting.

Cartridge Cases—What Works, What Doesn’t

When fired, the cartridge case “swells” against the walls of the firing chamber. Brass cartridge cases have been used since the mid-1800s when metal-cased ammunition became the ammunition of choice and firearms were both converted and new, built to fire it. Brass is easy to form and is a relatively soft metal. Its ductility allows a swelled casing to be easily extracted from the firing chamber. It also allows easy re-sizing in the reloading process. However, brass has become increasingly expensive in modern times, driving the ammunition industry to use other materials for cartridge cases.

Following WWII, the USSR developed the ability to form steel cartridge cases. This advancement in ammunition construction is noteworthy because steel cartridges swell differently than their brass counterparts. Steel also rusts, and it isn’t nearly as ductile as brass, making extraction of a spent (swelled) round more difficult. The solution was to coat each steel cartridge case with a thin lacquer film. The lacquer serves two purposes. First, it prevents rust. Second, it liquefies under heat and pressure when the cartridge is fired and works as a lubricant to aid extraction of the expended case. Brilliant! Russia produces steel-cased ammunition today in a variety of rifle and pistol calibers. This ammunition is far less expensive than brass-cased ammunition and works as reliably in most modern rifles and pistols.

In response to DoD’s requirement to lighten the soldier’s load, the ammunition industry is also pursuing both aluminum-cased and polymer-cased cartridges. Aluminum-cased pistol ammunition is available on the civilian market with comparative performance to brass-cased ammunition of the same caliber. Polymer-cased ammunition is still being refined. Its technical maturity suffers primarily from extraction problems where casings separate upon extraction, leaving some or most of the casing lodged behind in the firing chamber. Such problems will no doubt be overcome with material design refinement, but for now, polymer-cased ammunition is not ready for combat primetime.