By Paul Evancoe

In the world of firearms, the term “lockup” does not refer to convicts serving time.

Many gun owners who have heard the term lockup find it ambiguous and use it ambiguously with the term “in battery.” While these two terms are related, they are not, in general, interchangeable or synoptic by definition. For the purpose of this article we will explore the meaning of both terms and how they apply to firearms, with a focus on lockup.

In short, lockup is a mechanical action that occurs according to a firearm’s principle of operation. Lockup is often interchanged with “locked breech” and “in battery.” In our case, lockup refers to the locked firing position of a fully closed or “locked” bolt/action of most non-blowback, self-loading and manually loaded firearms, including pistols, rifles and shotguns. Once lockup is physically achieved, the action is referred to as being in battery. “Out-of-battery” refers to the status of the firearm before the action has returned to the normal firing position and lockup has been achieved. While that might all sound a bit confusing, in reality, it isn’t. Let’s first explore the origin of the terms beginning with “in battery.” The term can be traced back to the modern use of artillery in warfare. A field artillery battery generally consisted of five cannons, usually arranged in a line with their enemy-facing muzzles projecting into an embrasure, or over a parapet, in readiness for firing. Aligning the cannon muzzles in battery provided several advantages then, as it does today. It helps to keep the muzzle blast forward of the artillerymen who load and fire the cannons, and in the day of black powder, it kept that large cloud of smoke mostly forward of the cannons so the artillerymen could see what they were doing.

When fired, the muzzle loading cannons of the day would recoil and “travel” rearward, thus putting them physically out of firing alignment with the other cannons. They were, at that point, out-of-battery. At this location the artillerymen would reload the cannon then roll it back into its firing position in battery alignment and fire the next round.

This is the basis for the in-battery definition used today in the world of firearms. It means the recoiling mass of the weapon—e.g., bolt, slide, carrier and so on—is in the proper firing position. When the weapon is out-of-battery, the weapon’s recoiling mass has not returned to its proper position after firing because of a failure in the recoil mechanism, a spent cartridge extraction jam, a feed failure (or stovepipe) or other weapon malfunction that prevents physical alignment of the gun’s firing train.
About now you’re thinking, where does lockup fit into all these moving parts? Lockup refers to the weapon’s physical posture when the slide or bolt has fully returned to the weapon’s fully closed and locked position.

If the bolt rotates upon closure, as most do, lockup is achieved once the bolt’s locking lugs are fully engaged and rotated. At this point the most frequently asked question is: Can a gun still fire if it’s in battery but not fully locked up? The answer is, it depends upon the weapon’s design. Most of today’s firearm designs generally prevent this from occurring; however some do not, especially some of the older auto-loading machinegun designs.

There is another critical issue that comes into play at this point, and that is “headspace”—the space between the bolt face and the cartridge base when the cartridge is fully installed in the firing chamber. Adjusted by screw notches (clicks) in the barrel, because it will fire when the trigger is pulled even if it’s not in full lockup, the Browning M-2 .50-caliber machinegun is a prime example of the necessity to attain critical headspace. For the M-2, this is also known as “timing,” because the timing between lockup and firing must be set via the headspace to ensure the cartridge is fully inserted into the M-2’s firing chamber.

Guns with changeable barrels all have critical headspace issues. Most machineguns with non-headspace adjustable replacement barrels (M-60, M-240, M-242, etc.) come with two barrels that have factory-fitted headspace for that particular weapon. Contrary to popular belief, the spare barrels that come with one gun are not interchangeable with another of the same type, because the headspace is different between the two guns. Even so, operators will regularly mix and match barrels between guns of the same type out of naiveté, and that results in operating failure as well as an operational safety risk to the operator.

Most fixed-barrel guns have fixed factory-set headspace so lockup is a lesser issue for those designs. Today’s assault rifles and machine guns with quick-change barrels (QCBs) are all designed with preset headspace and require no headspace adjustment to achieve proper lockup.

Back to lockup. If a gun fires while it is not fully locked up, you’re holding/operating a very dangerous device. In both auto-loading and manually operated mechanisms, a condition can occur in which a live round is partially inserted into the firing chamber and capable of being fired. This condition can result from faulty headspace, from insufficient lockup, or both, and the result is the same when fired. The gas pressure produced at the moment of firing can rupture the not fully supported (chambered) cartridge case, and that can result in superheated flame and high-pressure gas being vented at the breech of the weapon.

This venting is threatening to both the operator (especially to the face and hands) and those close by, because it often creates flying shrapnel and injury. Micrometers and feeler gauges are not required to identify this problem. A tell-tale way is to simply inspect your spent brass. If the base-end of your spent cartridges is visibly swollen, cracked or split open, you most likely have a lockup problem that needs attention.

Like long guns, handguns suffer from insufficient lockup as well. In modern semi-automatic handgun designs, most will simply not fire upon pulling the trigger when not in a lockup state. That’s good news from a safety perspective but bad news from a reliability perspective if you’re betting your life on your gun’s reliability to fire when you need it most.

So what are the most often seen root causes of insufficient lockup? The general answer across-the-board is insufficient lubrication on critical friction points like slide rails, roller bearings, bolts, bolt carriers, etc. In general, the best preventative is to keep the friction points on your firearms well-lubricated and clean. In the field, adequate lube is more important than clean. Be mindful that not all lubricants are created equal. Applying the proper viscosity lubricant on the appropriate wear point is key. For example, light spray lubes are not necessarily adequate for areas exposed to high heat and heavy friction. Guide rails require higher viscosity lubricant than, for example, an extractor or firing train.

The secondary cause preventing full lockup can many times be attributed to a weak or broken recoil or buffer spring. In this case the tell-tale clue is the inability of the bolt or slide to consistently complete its forward stroke and return to its lockup firing position. Recoil springs do have a life expectancy, and they do wear out. Depending upon your particular weapon’s operating system, replace these springs as part of your scheduled maintenance plan. Don’t wait until your weapon fails to lockup in the middle of a gunfight.

A third lockup failure cause is the presence of foreign debris fouling the ammunition or the gun’s operating system, thereby preventing the cartridge from fully chambering. Weapons and ammunition exposed to grit, mud and sand, even ice, can be the cause. This condition is especially dangerous because an internal barrel obstruction usually results in the weapon blowing up in your hands in some form. Be constantly aware of the physical environment where you drag, carry and lay your gun(s) and spare magazines. When in doubt, unload your gun and sight through the barrel to ensure it’s clear of obstruction.

A fourth cause can be attributed to a “hard” mag change. This means the gun was ready to fire. It was in lockup, but when inserting the magazine and slamming it up into the magazine well, the bolt, or slide, moved slightly backward, compromising its lockup integrity. No longer in lockup, the gun cannot fire. The remedy is to ensure your magazines all fit properly into the weapon and the magazine catch firmly engages the magazine. If the slots in your magazines that the magazine catch engages are visibly worn or dented, replace the magazine with a new factory magazine. Worn magazine catch slots will allow the magazine to exceed its design-installed height when it’s slammed home, and that is a lockup malfunction waiting to happen. Carefully inspect all your magazines and throw away your damaged mags. Don’t keep them around for range use or spare parts. Get them out of your duty inventory permanently.

Finally, lockup integrity, as you have learned above, is paramount to reliable and safe firearms operation. Be vigilant and remain mindful of the symptoms leading to lockup degradation and failure. Keep your gun and magazines clean and properly lubricated. Replace faulty springs before they fail. Throw out all magazines that show damage or excessive wear around the magazine’s catch slot. Occasionally inspect your spent brass for swelling and splitting at the base end. These simple measures will serve to save your life.

This article first appeared in Small Arms Review V21N2 (March 2017)
and was posted online on January 27, 2017


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