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The 9mm Automatic: A Better 9mm Cartridge

by Brad Miller, Ph.D.   |  March 26th, 2014 133

The 9mm Luger cartridge is flawed. It has been flawed since its development around 1902 by Georg Luger for his famous Luger pistol. Since then, the 9mm Luger—also known as the 9mm Parabellum, 9X19, 9mm NATO or just the 9mm—has become one of the most popular cartridges on the planet. It is chambered in handguns, submachine guns and rifles, and is the standard NATO round for handguns. Frank Barnes (2006) notes that it is the most widely used cartridge in the United States.

The 9mm Luger has become especially popular for small, compact carry guns intended for self-defense. It is a potent cartridge for its size and offers good performance with well-designed bullets.

But the cartridge has a troubling flaw: it’s tapered.

This figure shows a prototype 9mm Automatic cartridge along with a 9mm Luger cartridge.  The difference in the shape of the case is not obvious, because the 9mm Luger’s taper is slight. But when the cartridges are placed along side their peers, the shape of the 9mm Luger’s taper becomes obvious by producing a gap between the rounds at the case neck.  The straight-walled 9mm Automatic produces no gap.

Taper increases a problematic behavior called nosedive. Nosedive occurs when the nose of the cartridge cams downward while being pushed forward out of the magazine during feeding. This causes the bullet nose to hit low on the feed ramp and at a more perpendicular angle. A tapered cartridge exacerbates nosedive, and the more a cartridge nosedives, the more likely it will cause a feeding malfunction.

Nosedive is an inherent problem in most single stack magazines. Even straight-walled cartridges nosedive, but cartridge taper makes it worse. Nosedive is less problematic in double column magazines, but it depends on specific magazine designs.

Not all 9mm Luger ammunition has the same amount of taper. Taper is defined as case head diameter minus case neck diameter. SAAMI 9mm Luger specifications show a taper of 0.010-inches (head to case neck; 0.014-inches for rim to case mouth). Samples of 15 different factory loads in the author’s possession had an average taper of 0.0094-inches. The least amount of average taper was 0.0065-inches and the most was 0.0135-inches. Within any given box of ammunition the amount of taper was relatively consistent.

The taper affects cartridge angle when they are stacked together, as shown below. These rounds are not positioned as they would be in most magazines, but it illustrates how the 9mm Luger’s taper contributes to cartridge angle. The straight-walled 9mm Automatic doesn’t produce this curvature.

The effect of cartridge taper becomes apparent when rounds are loaded in a magazine. When loading a single column magazine, a gap also will eventually appear between the front of the top round and the one under it. This is called the nosedive gap. As more rounds are added, the nosedive gap gets bigger.

The nosedive gap appears with straight-walled cartridges, but the 9mm’s taper can increase the gap by about one degree more than a straight-walled cartridge for every round added to the magazine (see slideshow). The taper on one side of a 9mm Luger cartridge is about one-half a degree. A larger gap means greater potential nosedive.

Attempts to change some aspect of the magazine or the follower produce limited results. But all these efforts have overlooked the obvious: All that is required for an immediate improvement in feeding reliability is to get rid of the taper, and here is the data to prove it.

Empirical Testing
I conducted extensive tests with a prototype cartridge that demonstrate clear benefits of creating a new 9mm cartridge with straight walls. The benefits are impressive. A straight-walled case dramatically improves cartridge feed angle and feeding reliability.

A prototype straight-walled cartridge was made from .38 Super Lapua cases, which are rimless versions of the .38 Super. The case wall and rim diameter of the .38 Super Lapua brass in the author’s possession was 0.381 inches, which nearly match the case mouth diameter of the 9mm Luger’s 0.380-inch SAAMI specifications. The prototype cartridge was made by trimming the Lapua cases to 9mm Luger length of up to 0.754 inches in length. When loaded, the prototype cartridge will be referred to as the 9mm Automatic (9mm Auto).

In concert with creating this prototype cartridge, functional tests were conducted to assess to what degree cartridge dimensions affect feed angle and feeding reliability. These tests examined cartridge taper and rim width.

I prepared special ammunition for these tests in order to maintain a similar overall length profile. The test ammunition, except for one factory load, was handloaded with Remington 115-grain FMJ round nose bullets to 1.160-inches overall length. Five different tapers were tested: no taper (9mm Automatic), .0037-, .005-, .0075- and .0133-inches. Brand new Remington 9mm Luger brass averaged 0.075-inches taper. These cases were not sized prior to loading in order to maintain their original shape of straight, non-parallel sides (sized 9mm Luger brass often results in “hour-glass” shaped loaded cartridges). The factory load was Federal 9mm Luger 115-grain FMJ round nose with a 0.0133-inch taper and an overall length of 1.156 inches.

The profile of the Federal round was very similar to the handloaded cartridges, and was used as an example of factory ammunition. The .0037- and .005-inch taper cartridges were made with once-fired 9mm Automatic brass.  When sized with a .38 Super size die, their average taper was 0.0037 inches because sizing did not remove all of the expansion from having been fired. A second group of fired 9mm Automatic cases was partially sized until they had a 0.005-inch taper.

Cartridge feed angle was measured from high-speed (1000 frames per second) video. Feed angle is defined as the lowest angle the cartridge achieves prior to hitting the feed ramp. The camera recorded cartridge behavior as it was stripped from the magazine. The test gun was a custom-built Caspian single column 1911 pistol with a ramped 9mm Luger barrel. A single McCormick .38 Super 10-round magazine was used for these tests. A .38 Super magazine positions the cartridge farther from the feed ramp than a 9mm Luger magazine. This condition permits maximum nosedive, which allows for an evaluation of the effect of different cartridge dimensions on feed angle. Also, some shooters (including the author) use .38 Super magazines in their 9mm Luger 1911 pistols.

A total of 240 rounds were video recorded and analyzed for feed angle. Three or six full 10-round magazines were run for each taper (9mm Automatic N=60; 0.0037 N=30; 0.005 N=60; 0.0075 N=60; 0.0133 N=30).

Feed angle for all cartridge designs is lower when more rounds are in the magazine. This occurs because the nosedive gap gets bigger as more rounds are loaded in the magazine regardless of taper. However, the nosedive gap is greater with tapered cartridges, and more taper means an even larger gap. The larger the nosedive gap, the greater the nosedive and the lower the feed angle.

In the figure below, the feed angle of the 9mm Automatic (black line) is at the top of the other lines at nearly every point, indicating a consistently high feed angle. The plotted values are the cartridge angle relative to the magazine feed lips. The angle of the tapered cartridges was adjusted in order to show the angle of the measured cartridge’s central axis on this and subsequent figures.

The important feature in the figure is the large difference in feed angle between most of the tapered cartridges and the straight-walled 9mm Automatic when there are four rounds and more in the magazine. The difference in angle can be quite large, up to over seven degrees (round 5) with the most tapered brass (0.0133). The 0.0075-inch tapered cases show a difference in feed angle of up to six degrees (round 6) from the 9mm Automatic. Even a taper as small as 0.005-inches produces a two-degree difference of angle with as little as 5 rounds in the magazine. The least amount of taper (0.0037) showed a feed angle similar to the 9mm Automatic.

Note the slight improvement in feed angle for some of the more tapered 9mm Luger cartridges with 9-10 rounds in the magazine. This is an artifact of it being a 10 round capacity magazine, as this improvement was not evident in a 15 round single column magazine that was tested. Presumably, when the magazine spring is near full compression, the pressure can affect the feed angle of tapered cartridges.

Several straight-walled .38 / 9mm cartridges exist which could be trimmed to 9mm Luger length to create the new 9mm Automatic cartridge. The .38 Super Lapua cases I used were truly rimless with the same rim and case wall diameter. Thirty-eight Super Comp (Starline) and .38 TJ (Hornady and Starline) are other “rimless” versions of the .38 Super cartridge.

However, they have slight rims that measure about 0.006-inches wider than the case body. By comparison, the .38 Super—which is semi-rimmed—has a rim diameter that is about 0.020-inches wider than the case body. The 9mm Steyr is another straight-walled case, and Barnes (2006) indicates a rim 0.001-inches larger than the case body. Actual rim width varies somewhat in all examples.

Rim width matters because the rim can enhance nosedive. The rim of the upper round is normally positioned in the extractor groove of the underlying round when they are in the magazine. During feeding, the slide pushes on the upper rim (base) of the cartridge. As the round is pushed forward, a rim wider than the case wall will drag on the underlying cartridge once it moves past the extractor groove. The push on the upper part of the rim and drag on the lower part of the rim combined with a nosedive gap encourages the cartridge to nosedive.

I tested several of these case designs trimmed to 9mm Luger length to assess the effect of rim width on feed angle. I selected cases with a rim of .0015-, .0025-, .006- and .020-inches wider than the case body.  Rim diameter measurements indicate rim diameter minus head diameter. Cases with rims less than .006-inches were carefully selected to ensure that the rim diameter did not vary more than .0005-inches depending on where it was measured. Cases were loaded with the Remington 115 grain bullet as described above. One hundred and twenty rounds (0.0015 N=30 Hornady 9mm Steyr; 0.0025 N=30 Hornady 9mm Steyr; 0.006 N=30 Starline .38 Super Comp; 0.020 N=30 Starline .38 Super +P) were video recorded and analyzed for feed angle and compared to the 9mm Automatic data.

The rims were not necessarily concentric with the case body.  That is, if the cases with minimal rims (.0015-.0025 inches) were slid along each other, sometimes the rim extended past the case wall diameter and would drag on the other case’s side wall, and sometimes it did not. Rotating the case to a different part of the rim eventually produced contact. Even the 9mm Automatic (.38 Super Lapua) cases did not have rims perfectly concentric with the case body, and some rim drag could be felt by this method.

I had no way to guarantee a consistent amount of rim drag during feeding. Thus, I left to chance the amount of the rim that would contribute to cartridge drag. Therefore, in some instances with these cases there would be rim drag on the underlying round and sometimes not. The rims on the 0.006 inch (and greater) rimmed cases always appeared to have some rim drag with the cases I examined.

Test results showed that wider rims produce lower feed angles (see slideshow). There was up to an eight-degree difference in feed angle (round 5) between the rimless 9mm Automatic and the cartridge with the widest rim (0.020). Even cases with a minimal rim (0.0015 – 0.0025 inches) showed an average decline of 1-2 degrees in feed angle for rounds four through eight. Keep in mind that in some instances there was likely no rim drag for these cases because of the reason mentioned above. The fact that there is some evidence of lowered feed angle in this group suggests that even a minimal rim will enhance nosedive. Thus, a true rimless case offers the best feed angle.

Feeding Reliability
I experienced no feeding malfunctions with the Remington FMJ round nose bullets during these tests. But as many shooters know, flat nose bullets can sometimes produce feeding malfunctions in guns that run round nose bullets reliably.

I tested two different flat nose bullets with three different cases for feeding reliability. The cases were Remington 9mm Luger (tapered), Starline .38 Super Comp (0.006-inch rim) and the prototype 9mm Automatic. The bullets were a Winchester 9mm 115-grain JHP seated to 1.115-inches, and a Speer 125-grain .357 SIG Gold Dot Hollow Point (GDHP) seated to 1.070-inches. Loads with 9mm Luger brass with the Winchester JHP bullet averaged 0.0068-inches taper and for the Speer .357 SIG GDHP bullet 0.0065-inches taper. The Speer .357 SIG GDHP bullet has an especially wide nose and was selected for that reason because wider bullets hit lower on the feed ramp, which can increase the chance of a feeding malfunction.

One hundred and eighty rounds were video recorded for this comparison (three full 10-round magazines (N=30) each for six conditions: three types of brass X two bullets). The feed angle with the two different bullets was very similar, so the lines are the average of the two bullets.

As one would predict from the previous results, the 9mm Automatic had the highest feed angles. The 9mm Luger had the lowest feed angles, and the 0.006-inch rim brass had intermediate feed angles. But more important was their feeding reliability. Some rounds experienced nosedive feed failures where the round stopped dead on the feed ramp.

The feed angles correlated with their feeding reliability. The 9mm Luger brass, with its lower feed angle, had problems feeding both flat nose bullets. The 0.006-inch rim, with its intermediate feed angles, had problems only with the wide-nosed Speer .357 SIG GDHP. But the 9mm Automatic cartridge, with its higher feed angles, experienced no feeding malfunctions with either bullet. Thus, the lower the feed angle, the greater the likelihood of a feeding malfunction. These results show the clear superiority in feeding reliability with the straight-walled rimless 9mm Automatic.

Feeding reliability was also tested with a Diamondback DB9. The nosedive angle of the top round in a fully loaded six round DB9 magazine with a tapered 9mm Luger and a straight-walled 9mm Automatic is shown below. The 9mm Automatic has a six-degree higher cartridge angle. The Diamondback magazine had the manufacturer’s “improved” follower designed to reduce nosedive.

Two bullets were tested in the DB9: a standard 9mm Speer 124-grain GDHP and the wider-nosed Speer .357 SIG GDHP. The loaded rounds had 0.011- and 0.012-inches taper, respectively, in Federal 9mm Luger brass. Both bullet designs fail to feed the top round from a fully loaded 6-round magazine. The bullet nose catches on a ledge in the frame below the barrel’s feed ramp. This also shows the dramatic improvement in feed angle offered by the 9mm Automatic. When loaded in straight-walled cases, the wide-nosed .357 SIG bullet has a significant margin of clearance and feeds 100% of the time. This is an example of another single column pistol where the straight-walled 9mm Automatic provides a higher cartridge angle, which dramatically reduces nosedive and produces an empirical improvement in feeding reliability.

Test Firing
The prototype 9mm Automatic was test fired in a variety of 9mm pistols: Caspian 1911, CZ-75 B, Glock 19, Kel-Tec P-11, Para Ordnance P18-9 and a Walther P99. Bullets included round nose, 9mm hollow point and .357 SIG designs. Feeding, extraction and ejection were flawless.

9mm Automatic Dimensions
The proposed dimensions of the 9mm Automatic (see slideshow) are backward compatible with the 9mm Luger chamber. The last table shows the proposed dimensions and actual measurements from 9mm Luger ammunition for comparison. Only three dimensions need to be modified from the 9mm Luger: the case wall, rim and extractor groove.

The new 9mm Automatic cartridge should work well with 0.380 inch diameter dimensions. This matches the 0.380 maximum SAAMI dimension for the 9mm Luger case mouth. The rim of the new 9mm Automatic will necessarily be smaller than the 9mm Luger, but not by much. Rim diameters of 9mm Luger ammunition in the author’s possession ranged from 0.387 to 0.390 inches, so the proposed 0.380 rim diameter is within 0.007 to 0.010 inches and should not require extractor adjustment except in exceptional cases. The prototype Lapua cases had a 0.381-inch rim and functioned in all pistols tested. The extractor groove waist dimension must also be reduced to maintain the same extractor engagement.

Dramatic Improvements
A straight-walled rimless 9mm cartridge provides a clear benefit for feeding reliability in single column pistols. With the abundance of these pistols produced today, especially for the self-defense market, maximizing reliability is a compelling argument for its creation. My tests document a dramatic improvement in cartridge feed angle, and restored feeding reliability with flat nose bullets. It is by far the most practical solution to overcome the flaw of the tapered 9mm Luger design.

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