.45 ACP Headspacing and Case Length

Watching a Model 1911 .45 ACP pistol cycle in slow motion, with the aid of high-speed photography, is nothing short of spectacular. As the trigger is pulled, the hammer falls, striking the firing pin, which is driven forward into the primer of the cartridge in the chamber, firing it. At this point the barrel stays locked just long enough to allow the igniting cartridge to get over its peak pressure point, which is unbelievably quick! The fired case pushes back on the slide hard enough to move it and the barrel rearward. The barrel link pulls the barrel downward to disengage its locking lugs from the recesses in the slide (and barrel movement stops).

The slide, which houses the extractor, continues to move to the rear and pulls the case from the chamber, then the frame-mounted ejector bumps the case out the ejection port. As the slide moves rearward, it cocks the hammer and pushes the disconnecter downward to disconnect the trigger from the sear. As the spring-loaded slide returns home, it picks up a new cartridge from the top of the magazine, slides the rim of the cartridge under the extractor and drives the cartridge into the chamber as the barrel locking lugs snap into battery. Almost instantly the old war-horse is ready to fire another shot.

While I have left out some of the detail of the complete Model 1911 cycling process, let’s just recognize that it represents a blend of timing between gun and ammunition that must be correct, or reliability and even safety can suffer. This also holds true for other autoloading .45 ACP pistols.

An area of assembling .45 ACP ammunition that is occasionally misunderstood is headspacing. As outlined by SAAMI specifications, this cartridge headspaces on the mouth of the case. In other words since the case is a rimless design, the mouth contacts the headspacing shoulder of the barrel, or the end of the chamber, to prevent it from being chambered too deeply. If cases are too short or have been roll crimped excessively, rather than taper crimped, they will chamber too deeply, possibly causing misfires, or at the very least resulting in inconsistent ignition and poor accuracy.

Furthermore, manufacturers such as Colt, Smith & Wesson, Ruger, Kimber, Glock and others build their pistols to headspace on the case mouth, not the extractor. This is not new, as .45 ACPs have been designed this way for nearly a century. For example a Colt Government Model 1911 of World War I vintage was disassembled, and a Remington Ball factory loaded cartridge was slid under the extractor. The barrel was pushed into the slide and then over the cartridge, and the lugs were engaged. This is the same position the cartridge, slide and barrel are in when the pistol is ready to fire. (This was the slide and barrel assembly only!) The case length (not cartridge length) on this factory load was .892 inch and was within SAAMI specifications. There was a .030-inch gap between the “face” of the extractor and the forward edge of the cartridge rim.

Several more Model 1911 .45 ACPs were checked using this same (or similar) method, including a Series ‘70 and a Series ‘80 Colt Government Model, a Kimber Custom Classic Model 1911 and a Kimber Pro Carry. The gap between the case rim and the extractor, a very difficult spot to measure, varied slightly from .022 to .035 inch, or about .013 inch variance, an insignificant difference. (Not bad for guns built over an 85-year period!)

In each instance the extractor did not touch the rim when the cartridge was fully chambered, the slide closed and the barrel lugs engaged. The point being that the extractor has nothing to do with the headspace, as long as ammunition is used that is within specifications. A space of .020 inch minimum is required for the cartridge rim to slide at a tilted angle under the extractor, as the cartridge is stripped from the magazine and the bullet turns upward and starts into the chamber. Likewise single-action revolvers that are chambered in .45 ACP must headspace positively on the case mouth to prevent cartridges from dropping into the chamber too deeply and misfiring due to excess space between the firing pin and primer.

Handloads containing cases that have been trimmed excessively short, or shorter than recommended by SAAMI, will headspace incorrectly on the extractor. For example, I took a small quantity of .45 ACP brass and trimmed them back to .843 inch, or .045 inch shorter than is recommended. They were then primed and charged with 5.7 grains of Winchester 231 and a 230-grain Speer bullet was seated and taper crimped with an overall cartridge length of 1.265 inches. Again, the above guns were disassembled and a cartridge slipped under the extractor and the barrel installed. With the cartridge pushed as deeply as it would go into the chamber (with the aid of a small screwdriver), these out-of-spec cartridges headspaced on the extractor. I should point out that where the base of the cartridge would normally be positioned snugly against the breech face, there was a significant gap.

Next I fired these “short” cartridges in a Series ‘80 Colt Government Model. All the cartridges fired, but accuracy was poor, and primers revealed that cases were resting at various depths (in the chamber) at the time of ignition. Naturally the force of the firing pin impact on the primers varied considerably as well. In a Ruger Blackhawk .45 ACP revolver, they wouldn’t fire at all but did indicate some slight firing pin impact on the primer. Across the chronograph, this load, which duplicates factory ballistics and usually has an extreme spread of about 20 fps, produced velocity spreads that were much greater.

In order to assemble reliable and accurate .45 ACP handloads, cases should not exceed maximum case length of .898 inch, and if they need trimming, reduce their length to no less than .888 inch. For the most consistent primer ignition and velocity, cases should be trimmed to equal lengths.

While it has been published several times that the .45 ACP needs no crimp, I disagree. When the slide of a Model 1911 slams forward and picks up a round from the magazine, the inertia alone (not to mention the bullet slamming into the feed ramp), has been known to cause the bullet to seat deeper into the case and rest on the powder charge. If the bullet-to-case fit is not particularly tight, especially when using 230-grain cast bullets, this potential problem can easily occur. (Certain older dies either failed to size cases down far enough or had an excessively large expander ball, which invites this problem.) A bullet that is properly crimped, along with a tight bullet/ case fit, greatly reduces the chance of this happening. As previously stated, the crimp should be a taper crimp, rather than a roll crimp, so the case mouth still makes positive contact with the end of the chamber, or headspacing shoulder. The crimp should measure .470 inch diameter at the forward edge of the case mouth.