Headspace: Exactly What Is It Anyway?

Headspace. Is it bad? Is it good? Do I need any? Can I get some to go? How do I check it? How do I fix it? As a working gunsmith and an ammunition remanufacturer, I’m intimately familiar with and particularly interested in headspace concerns; and in this report, I’ll attempt to clear up what I see as a great deal of confusion. What the Dickens Is Headspace? First, we need to know some basics.

Headspace, defined in its most basic terms, is simply the distance between the breechface (when in battery) and whatever part of the chamber stops the cartridge from entering the chamber any farther. In the earliest self-contained-cartridge firearms, this was usually a rim on the case’s head. The term is derived from the practice of measuring the distance from the breechface to the breech end of the chamber—the space occupied by a cartridge case’s head. Thus, we have head plus space equals headspace.

So, you can see that, in order to function, any cartridge weapon must have some headspace; otherwise, cartridges would not chamber. The proper headspace is important for both safety and performance concerns. We’ll look at the safety issues first: Insufficient Headspace. This can mean a couple of things. Usually, when an insufficient-headspace condition is encountered, the bolt will not close on the cartridge.

However, it is also possible that the chamber is improperly cut or that a physically defective or out-of-spec cartridge (or the wrong cartridge!) is present. Any of these could lead to serious pressure problems should they not permit the case neck to release the bullet properly. Excessive Headspace. This condition can occur from the same set of problems as insufficient headspace (chamber improperly cut, physically defective or out-of-spec cartridge, wrong cartridge, etc.) and presents a wide range of difficulties.

From a safety standpoint, excessive headspace means that there is enough space for the solid case head to move back against the breechface and expose a thinner part of the case to an unsupported area, inviting a blown case or ahead separation. Excessive headspace often leads to blown primers as well. Blown cases or primers and head separations lead the shooter to believe that the ammunition is "too hot," while it is actually the firearm that has a problem.

Okay, insufficient and excessive headspace are understandable enough, but how does headspace affect performance? • Shot-to-shot uniformity depends a good deal on consistent ignition of the powder charge. The powder is, of course, ignited by the primer. The rapidity with which an explosion develops its maximum pressure (called brisance) is directly related to how hard the primer is struck by the firing pin.

If you follow this trail of bread crumbs, you’ll see that inconsistent cartridge placement in the chamber can lead to unpredictable firing-pin strike intensity, which causes variations in powder ignition, which in turn produces erratic performance. If headspace is excessive, misfires can occur because the primer is not struck hard enough to ignite.

Ironically, this sometimes shatters the priming pellet, making it impossible to subsequently fire the cartridge and leading the shooter to believe that the ammunition is faulty. • Haphazard cartridge placement in the chamber can cause bullets to enter the bore slightly misaligned, causing "variable accuracy." • Long chambers for all bottle-necked case cartridges stretch and over-work the brass case. This leads to very short case life and premature case failure for reloaders.

While headspace means the same thing regardless of the type of cartridge used, the exact points of reference are different with different cartridge types. In order to understand headspacing concepts, you must first understand the types of cartridges and how each type’s position in a firearm’s chamber is controlled. There are two basic types of car

tridges, both of which are comprised of several subcategories. I’ll examine these cartridge types next. Basic Cartridge Type #1: Rimmed, Semi-Rimmed, or Belted The easiest-to-understand cartridge type is the rimmed cartridge.

Rimmed cases come in four types: • Straight-walled, rimmed (.38 Special, .45 Colt, .45-70 Government, .22 rimfires, shotgun shells, etc.) • Straight-walled, semi-rimmed (.25 ACP, .32 ACP, .38 ACP, .38 Super, and the family of obsolete Winchester Self-Loading cartridges) • Bottle-necked, rimmed (.38-40, .44-40, .303 British, .30-30, .30-40, 7.62x54R, .17 rimfires, etc.) • Bottle-necked, semi-rimmed (.220 Swift, .307 Winchester, .356 Winchester) Straight-Walled Rimmed Cartridges.

These cases were among the earliest developments in the self-contained cartridge race. The earliest rimmed cases were of the rimfire design. As power needs grew (along with a demand for an easily reloaded case in areas far from fresh ammunition supplies), centerfire cartridges took over center stage.

The natural pairing of the rimmed case with Rollin White’s bored-through cylinder (the patent for which was purchased by the young Smith & Wesson Company) was the first giant leap toward a truly practical repeating handgun. Chambers for rimmed-case cartridges are often cut rather generously, since the chamber’s dimensions have nothing to do with headspacing the cartridge. Chambers for straightwalled cases need only be marginally longer than the case.

This is what allows .38 Special ammunition to be fired safely in a .357 Magnum chamber, 2-3/4-inch shotshells in 3or 3-1/2-inch chambers, and so on. (Don’t try this with bottle-necked case cartridges except under certain very narrow parameters, like fire-forming cases or firing standard cartridges in an "improved" chamber.) Straight-Walled Semi-Rimmed Cartridges.

These have a rim that is slightly larger in diameter than the case, but proportionally much smaller than the rim on true "rimmed’ cartridges such as the .38 Special. There are three common ones (.25 ACP, .32 ACP, and .38 Super Automatic), and several obsolete ones. Other entries in this category include the .38 ACP and the family of Winchester Self-Loading (WSL) cartridges (.32, .35, .351, and .401), all of which are long obsolete.

Official industry cartridge and chamber drawings show the case’s semi-rim as the headspace-controlling point for all these cartridges. Pistols chambered for the .25 ACP generally adhere to this rule, butting the semi-rim against the end of the chamber (just like a rimmed case). In .32 ACP, a mixed bag exists.

Older pistols, most imported pistols, and most inexpensive pistols use the semi-rim, some in the same fashion as the .25 ACP and some (such as the Colt 1903 Pocket Hammerless) having a countersunk shoulder in the chamber to catch the semi-rim. These arms treat the cartridge as a rimmed case. However, some modern arms chambered for the .32 ACP (the NAA Guardian, for example) headspace Figure 1. the cartridge on the case mouth as if it were a rimless cartridge.

The semi-rim serves another function for .25 ACP and .32 ACP pistols. Having spent some time studying Browning’s designs, I sincerely doubt it’s accidental. The extra diameter of the semi-rim assists feeding from the magazine and aiding extraction in the sometimes diminutive pistols chambered in these cartridges. The added size of the semi-rim tends to combat feeding problems such as those afflicting the rebated-rim cartridges and provides a much better "handle" for an extractor than a .22 rimfire case.

The .38 ACP has been obsolete for decades, and no modern arm is chambered for it. Pistols chambered for the .38 ACP used the semi-rim for headspacing, in one of the manners described above. All the WSL cartridges were used in arms that headspaced the round on the semi-rim, just as if they were true rimmed cartridges. The .38 Super Automatic, also known as the .38 Super, .38 Auto +Por .38 Super Auto +P, is also a semirimmed case but most arms manufacturers treat it as rimless.

The .38 Super is dimensionally identical to, but operates at around half again the

pressure of, the old .38 ACP cartridge. It was developed for use in the Colt Government Model pistol (which is enormously stronger than the earlier Colt 1900, 1902, and 1903 pistols designed for the .38 ACP). Most .38 Super pistols originally had a small relief step cut on the barrel hood or in the chamber intended to interface with the semi-rim of the case and provide a headspacing point.

In use, however, case and chamber tolerances usually combined to let the cartridge bypass the hood’s step, and the round ended up being held by the extractor or butting its mouth against the end of the chamber. This caused major accuracy problems. Urged on by intrepid experimenters such as George Nonte, manufacturers found a market for .38 Super pistol barrels that headspaced ammunition on the case mouth and ignored the semi-rim entirely.

This simple change in headspacing dramatically improved the Super’s accuracy, and it swept the shooting world for several years until cartridges with higher pressure limits came onto the scene. Colt finally got the picture in the 1980s and followed suit. Figure 2. Semi-Rimmed Bottle-Necked Cases. An oddball element of the bottle-necked cartridge family is the semi-rimmed .220 Swift, developed as a matter of simple expedience and introduced to the public in 1935.

When Winchester was looking to market the "ultimate varmint cartridge" in the early 1930s, they settled on using the old 6mm Lee Navy cartridge as a parent case. (It had an ideal case-volume to bore-volume ratio, called the expansion ratio, for propelling .22-caliber bullets at unheard-of velocities without excessive throat erosion—at least on paper.) They necked the case down from 6mm (.243) to .22, and the cartridge was a great performer.

However, the rimless 6mm Navy case had an odd-sized head which did not fit any standard bolt face—so Winchester simply added a small rim to the case that was the same diameter and thickness as the .30-06 family’s extractor rim. This neatly solved extraction problems and eliminated the need for either retool ing to make an odd-sized bolt face or retooling to produce a completely new cartridge case.

In use, the semirim serves only as an extraction aid, and has no bearing on headspacing; the cartridge is treated as a rimless bottle-necked case. The .307 and .356 Winchester cartridges are treated as rimmed cases. SAAMI classifies them as semi-rimmed due to the relatively small difference in rim diameter versus case-head diameter. They were designed to function through a Winchester 1894 action, and are simply .308 Winchester and .358 Winchester cartridges with a .30-30 WCF rim attached.

Savvy reloaders will treat them as rimless when reloading, taking care to not set the shoulder back. This improves case life and accuracy. Finally, we have belted cartridge cases, a variation of the rimmed cartridge. In this case, the belt can be considered a rim, just moved forward a bit. Belted cases come in the same types as rimmed cases: straightwalled belted (.450 Marlin, .458 Win Mag, .458 Lott, etc.) and bottle-necked belted (.300 H&H, .375 H&H, .300 Win Mag, 7mm Rem Mag, etc.).

Belted cases were developed by the British firm of Holland & Holland after the turn of the last century to solve two problems: containment for the high operating pressures of newly-developed smokeless-powder African-game hunting cartridges, and the necessity of having a solid headspacing point for those cartridges. A characteristic of H&H cartridges is a gently tapering case body with a shallow shoulder.

This shallow shoulder is hardly suitable for headspacing, as the blow from the firing pin tends to wedge the cartridge deeper into the chamber, detracting from reliable ignition. Nevertheless, the shallow shoulder is eminently practical for easy feeding and chambering of the cartridge and superior extraction of the fired case. The first successful example of a belted cartridge was the .375 H&H Magnum (1912).

The rim or "belt" provides a solid point to retain the cartridge when it is struck by the firing pin, ensuring proper ignition. Figure 1 illustrates both rimmed and belted straight-walled cases. Figure 2 shows both rimless and belted bottle-necked cases. Belted

straight-walled cartridges are much the same as their rimmed kin—.458×2" and .458 Win Mag cartridges can be fired safely in a .458 Lott chamber. Again, don’t even think about trying it with any bottle-necked case (with the possible exception of fire-forming cases or firing standard cartridges in an "Improved" chamber).

Basic Cartridge Type #2: Rimless or Rebated-Rim The other common cartridge type is the so-called "rimless" case and its variants. "Rimless" cartridges have what might appear to be a rim, but it is not; the diameter of the "rim" is the same size as or a few thousandths larger than the case head. This is actually just the end of the case after an extractor groove is cut in the case head.

This groove is simply a place for the weapon’s extractor to find a purchase on the cartridge case and has no involvement in headspacing these cartridges.

Rimless cases also come in two basic subcategories: • Bottle-necked (7.62×25 Tokarev, 7.65 (.30) Luger, 7.63 (.30) Mauser, .223 Rem, .308 Win, .30-06 Springfield, 7×57, 7.65×53, and 8×57 Mauser, among many others) • Straight-walled (.30 M1 Carbine, .380 ACP, 9mm, .45 ACP, etc.) Bottle-necked and straight-walled rimless cases each have a rebated-rim sub-type (.284 Winchester, the Winchester Super-Short Mag, Winchester Short Mag, Remington Short-Action Ultra Mag and Remington Ultra Mag cartridges; .41 & .50 Action Express, and .50 Beowulf).

Rimless Bottle-Necked Cases. The vast majority of rifle cartridges (and a few handgun cartridges) are of the rimless bottle-necked variety (Figure 2). Rimless bottle-necked cases area direct result of experimentation with smaller-bore, bolt-action rifles and smokeless powders. Rimless cases feed more smoothly (especially from a box magazine) than their belted or rimmed counterparts.

The earliest successful rimless bottle-necked case examples that come to mind are the 1888-vintage 8x57mm German Commission Rifle cartridge, the 1889-debuted 7.65x53mm Mauser cartridge designed for the Belgium-made Mauser rifle (commonly called the 7.65mm Argentine), and the 7.5x55mm Swiss. Rebated-Rim Bottle-Necked Cases. An unusual offshoot of the rimless bottle-necked family is the rebated-rim bottlenecked case, which has a "rim" that is actually smaller in diameter than the case.

The most readily recognizable standard cartridge of this type is the .284 Winchester. It has a diameter immediately in front of the extraction groove almost as large (0.500) as a standard belted case’s body forward of the belt (0.513). This gives the case more volume for a given length than would otherwise be possible. The extractor "rim" is the same size as the .30-06 family, meaning a standardized bolt can be used. There are a growing number of rebated-rim cartridges, with new ones sprouting regularly.

The Remington Ultra Mag cartridges, Remington’s Short-Action Ultra Mags, Winchester’s Short Magnums, and Winchester’s Super-Short Magnums are the most significant members of this category. Rebated-Rim Straight-Walled Cases. The .41 Action Express, .50 Action Express, and .50 Beowulf are rebated-rim straight-walled cartridges.

A variation in theme from the bottle-necked rifle version, this is done for the same reason as in rifle cartridges—to allow a larger-diameter bullet to fit in a case with an existing-size extraction Figure 3. rim. The .41 AE uses a case diameter suitable for a .41-caliber bullet, but will still fit into a 9mm-size magazine. It has the same extraction rim diameter as the 9mm Luger. The .50 AE’s story is very similar.

It has an extraction rim identical to the .44 Magnum, but its case body is large enough to handle .50-caliber bullets.

The .50 Beowulf shares a common extraction rim size with the M43 Russian cartridge (7.62x39mm) to allow its use in specially-barreled AR-type rifles equipped with a 7.62×39 bolt. (This is about the largest practical size cartridge case and bolt face for a standard AR-type rifle.) While this may seem like a great idea in theory, in practice the smaller case rim can cause problems when feeding from a magazine.

Unless the magazine presents the cartridge high enough to keep the rim in constant contact with the bolt or breechface while the round is stripped from the magazine, a rebated-rim cartridge sometimes exhibits a tendency to dive under the bolt/breechface before the magazine releases the case during the feed cycle, causing a "bolt-over" jam.

Headspacing Rimless Bottle-Necked Cases Headspacing rimless bottle-necked cartridges is accomplished by using an agreed-upon point of reference on the chamber’s neck to arrest the case’s forward progress into the chamber. This point is called the "datum line." Essentially, it is the point at which the chamber’s neck is a given diameter. This point differs from one case family to another. For example, the .30-06’s

shoulder isn’t in the same place or at the same angle as the 8×57 Mauser’s, so they have different datum line measurements—both in diameter at the datum point and in its distance from the breech. Most cartridges used in semi-automatic pistols are rimless "straightwall’ designs. There are, however, a number of notable exceptions.

Some, such as the newer .400 Cor-Bon and .357 SIG, wildcat numbers like the old .38-45, and an aging trio of military cartridges (7.63×25 Mauser, 7.65 Luger, and 7.62X25 Tokarev) are rimless bottle-necked cartridges, and headspace the same way as their rifle-cartridge kin.

Headspacing Straight-Walled Cases Straight-walled cases, whether rimless and rebated-rim, are headspaced by having the shoulder at the front of the chamber sized and shaped such that a properly-crimped case will not wedge into the chamber throat (the area immediately in front of the chamber, before the rifling starts). See Figure 3. The case mouth is used to stop the cartridge’s forward movement. What Happens When A Cartridge Is Fired?

Understanding what occurs when a cartridge is fired in a weapon’s chamber is essential to understanding the importance of proper headspace. Referring to Figure 4, when the primer is fired, it backs out of the primer pocket with considerable force.

The case is rammed into the chamber both by the firing pin’s blow and the primer’s expulsion. (This is the reason why rimless bottle-necked cartridges need a well-defined and substantial shoulder; a case with a very gentle shoulder would tend to be driven into the chamber when the firing pin strikes, causing a variety of problems from misfires to blown primers to high pressure spikes from the case mouth becoming wedged in the chamber throat and thus being unable to release the bullet.) This is the mechanism that causes flattened primers.

It’s important to understand that primers can be flattened by excessive headspace with pressures in a normal range. Case-head expansion is a much more reliable indicator of pressures than primer condition. Now look at Figure 5. As pressure builds and the bullet begins to move, the case swells against the chamber, sealing the breech from the burning propellant charge. The case seals from the front backward, because it is thinnest and softest in the neck/ shoulder region.

Figure 6 illustrates the next step in the process. The head of a cartridge case is much harder and thicker than the neck/shoulder area, and does not swell to the same degree in the Figure 4. Figure 5. Figure 6. Figure 7. chamber. As pressure rises towards peak levels, the tensile strength of the brass case is exceeded. The case stretches to the breechface, reseating the primer in the process.

This is what causes case-head separations: The case stretches in the only place available, immediately in front of the solid head. Note: It might be useful to remember that if a cartridge does not develop sufficient pressure, it will not swell and/or stretch much. Very low pressures can produce protruding primers and look (to the untutored eye) like a high-pressure problem because of the protruding, sometimes flattened primer and the stiffness or complete lockup of the action. Protruding prim

ers will lock up a weapon’s action like an overpressure round, but they do so because the primer’s initial explosion has wedged the case firmly in the chamber and the primer was not reseated—thus, no headspace! You’ll see this with old smokeless-powder ammunition which has been stored improperly; smokeless powder loses its chemical energy and simply does not perform after it deteriorates. Basically, you’re left at Figure 4, with no bullet. Now to Figure 7.

After the bullet has left the muzzle and the bore pressure drops, the brass case shrinks a bit. This allows easy extraction of the fired case (unless the chamber is misshapen or rough). Very high pressures cause sticky cases, partially because the brass is stressed beyond its elastic limits and partially because the chamber swells under the strain, allowing the brass to stretch to the point that it is still wedged firmly in the chamber after firing.

Go, No-Go, and Field Gauges First, a few notes on factory-loaded ammunition. There are dimensional tolerances for ammunition, just like for firearm chambers. Ammunition generally has allowances for dirty and tight chambers. Additionally, the elasticity of the brass case and its ability to rebound (after firing) to a size small enough to allow easy extraction means that factory ammo is usually loaded to the smaller side of allowable dimensions.

If you use cartridge-case headspace gauges when reloading, you’ll note that factory ammo will often fall well below the minimum-length step on the gauge. You’ll also see why it’s not a good idea to check headspace with a factory cartridge, as factory cartridges can be as much as 0.006 to 0.010 inch shorter than the industry-specified minimum chamber headspace dimension and still be within production tolerances.

Add those few thousandths to the extra space in a very long chamber, and you’ll see why a thorough understanding of proper headspacing is important. Anyone who advocates using factory ammunition and shims as headspace gauges doesn’t have a clue about the critical importance of proper measuring tools, and is potentially dangerous to himself and to others. Now that you know what headspace is, I’ll cover the gauges used in determining the headspace condition of a firearm and how it’s measured.

Although match shooters and many custom gunsmiths have multi-gauge sets (for one cartridge family) that range from minimum to maximum, I’ll stick to three standard measurements—go, no-go, and field (or field reject). Ago gauge is dimensioned as an industry-standard minimum headspace dimension. For rimless cases, this is the shortest chamber that will safely handle ammo loaded to maximum industry dimensional specifications.

For rimmed/belted cases, this is the minimum rim clearance space that will accept ammunition loaded in cartridge cases with an industry maximum thickness rim or belt. A no-go gauge represents a maximum recommended-length headspace dimension. For rimless cases, this is the longest chamber advisable in order to safely fire ammunition loaded to minimum industry dimensional specifications.

For rimmed/ belted cases, this is the maximum rim-clearance space that will safely accommodate ammunition loaded in cartridge cases with an industry minimum thickness rim or belt. Afield gauge represents the largest safe headspace dimension allowable. Although readily available for a wide selection of cartridges, field gauges are generally used for military or ex-military cartridges such as the .30-06, .303 British, and 7 and 8mm Mauser used in military or ex-military arms.

Military armorers call it a "field reject" gauge, because it represents the longest safe headspace dimension allowable for use with military ammunition, which generally has a thicker case head than commercial ammunition. Military arms often have chambers on the large side for reliable function under adverse conditions and with all types of ammunition.

It’s not at all unusual for a military weapon to chamber (or nearly chamber) a no-go gauge, even in brand-new condition—and it will be perfectly safe to use as long as the proper military ammunition is used. Any firearm which will chamber afield gauge should not be fired until the problem is corrected. It is a normal practice to make standardized cartridges in a given family share a common datum point.

Thus, the .25-06, .270, and .30-06 all share a common measurement from datum line to breechface, which means that they all use the same headspace gauges. The datum line for this family of cartridges (all based upon the .30-06 as a parent case) is specified as a circle 0.375 inch in diameter on the case shoulder’s taper. Minimum distance allowable from this point to the breechface (go) is 2.049 inches; a chamber shorter than this is considered to have insufficient headspace.

Maximum length acceptable from this point of the chamber’s shoulder to the breechface (no-go) is about 2.053 inches (plus 0.002 inch or so, depending on the gauge manufacturer’s adopted standard). Beyond this length, the chamber is considered to have a possible excessive headspace condition. The field reject length for this family is 2.059 inches; any chamber 2.059 inches or more from breech to datum line is dangerously long and corrective action needs to be taken.

These ranges of 0.003 to 0.005 inch between go and no-go and 0.006 to 0.010 inch from go to field are common for most cartridge types. (There are exceptions, variations, and oddities, however, especially with proprietary cartridges.) The higher a cartridge’s intensity, the more critical proper headspace becomes. Under ideal conditions, a firearm’s headspace should be between go and no-go gauge sizes. A headspace larger than no-go in a sporting weapon should be addressed before any further use.

While a good many firearms function perfectly well with headspace between no-go and field, the resultant case stretching at the head may eventually lead to a blown case, blown primer, or ahead separation.

It will definitely result in extremely stretched cases and head separations for the novice reloader. A military arm using only military ammunition (or reloads in military cases) can safely function until its headspace reaches the field dimension, at which point it will need service (hence the name "field reject").

I don’t recommend using commercial ammunition or reloads using commercial brass in any weapon which has headspace larger than no-go, because of the fact that commercial brass as a rule has thinner case heads than military brass. Consider the tolerance stacking I’ve described, and you’ll see that it’s possible to have a dangerously gross long-headspace condition where total clearances can be 0.020 inch or more. This represents a case rupture or blown primer just waiting to occur. Where Did It All Go?

It’s a fact that headspace grows as a direct function of how much an arm is fired and what type of ammunition is used. There are several reasons for this, depending mainly on the type of firearm. Revolver headspace growth has two major components—wear or battering of the bearing surfaces on both ends of the cylinder and frame stretching. Frame stretching occurs when the revolver’s strength limits have been exceeded by use of improperly selected ammunition.

Headspace growth in semi-automatic pistols rarely occurs to an extent great enough to become a problem. This is mainly due to the relatively lower pressures used in most auto-pistol cartridges. Excessive headspace is sometimes seen in inexpensive handguns that use an aluminumor zinc-alloy slide (without a steel breechface) due to breechface setback that occurs from the repeated pounding of normal use.

Headspace growth in rifles (and various handguns chambered for rifle cartridges) occurs as a result of wear and pressure. The wear is understandable, as anything with moving parts is going to encounter wear at some point. But pressure? Yes, indeed.

Here follows a rough depiction. (This example does not take the changing pressure curve or the bullet’s friction with the bore into account; we don’t need that kind of math to demonstrate what’s happening.) Consider a bullet being forced down a barrel by a gas at 50,000 psi. During that period, there is considerable force involved in pushing the bullet away from the receiver. (The exact force would depend on the bullet’s cross-sectional area).

For a standard .30-caliber bullet, the force on the base of the bullet would amount to approximately 3,725 psi. Receivers and bolts are, by necessity, either fairly hard or are surface-hardened on load-bearing parts. Barrels, on the other hand, are comparatively soft. As long as this force is acting on the bullet, it is essentially trying to push the barrel inside-out. Exactly how much of this force is involved in pushing the bore away from the chamber depends on the bullet’s coefficient of friction with the bore.

Over the course of firing thousands of rounds, this repeated stress actually stretches the chamber—and the barrel forward of the chamber—away from the breech. During a quality rifle’s life, the bolt and receiver will suffer very little deformation and/or wear to their locking surfaces, while headspace constantly grows.

It’s been suggested to me that the repeated slamming of cartridges into the chamber causes this headspace growth, but I reject that argument on Binder Ad (p/u from page 18, AGM-August 05) the basis of observed facts: • Brass is a whole lot softer than steel. The shoulder of a cartridge is not only softer yet, it’s very thin.

I really don’t see how the soft brass cases can damage a chamber when much harder bullet jackets don’t cause equivalent damage to a bore. • It’s a provable reality that two otherwise identical rifles will have much different service lives if one is fed a steady diet of high-pressure ammunition and the other is only fired with starting-level handloads—even if the same bullets, powders, primers, etc.—are used in both.

Headspace growth in shotguns develops as wear to various parts such as hinge pins and bolt-locking surfaces, and in part due to the general softness of the steel used for shotgun barrels. Shotguns use ammunition developing less than 15,000 psi (much lower than many handgun cartridges), and their barrels are usually soft. Conclusions Now that we understand what headspace is—and isn’t—and its critical importance, I’ll cover the actual process of measuring headspace in a followup article.

I’ll also examine the possibility of making your own gauges for oddball-type arms—assuming you’re a reasonably proficient machinist and have the extra time.■