Common CZ/DW Reloading Issues Related to 9mm Tapered Cartridges

[Wobbly]

Common Reloading Issues Related to 9mm Tapered Cartridges -
Jamming in the Chamber

A situation can arise that occurs only with the tapered 9mm pistol cartridge design. While being fired, a random cartridge enters the chamber half-way and jams the firearm. The slide cannot move forward "into battery" and allow the cartridge to be fired. Nor can the slide be reversed so that the cartridge can be extracted from the chamber. The gun is left in a "hot" condition and the safety cannot be engaged. This can add up to a very dangerous Out Of Battery (OOB) situation that may baffle even experienced reloaders.

This event happens mainly with the 9mm Luger, and only because of the tapered chamber. Other common cartridges (such as 38Spcl, 45ACP, 380Auto, and 38Super are "straight walled cartridges" and do not have the tapered chamber common to the 9mm series. The tapered chamber is the mechanism that allows the misshapen cartridge to enter half-way and then wedge itself into place, thus creating the locked slide event. Such an event is shown below...



This event is caused by one of 4 main problems:
 • Excessively long cartridge OAL   (Issue at the bullet's nose)
 • Poor taper crimp settings             (Issue at the case mouth)
 • Bullets seated too deeply              (Issue at mid-case)
 • Expanded case heads                     (Issue at the case head)

In each of these situations it's important for the gun owner to understand that correct cartridge-to-chamber fit depends upon clearances smaller than a human hair, in some places 0.001 to 0.002". Therefore, these obstructions cannot typically be seen with the naked eye and a strict reliance upon accurate measurements is essential to find and correct these issues.

NOTE: Although these issues are normally only found on handloaded ammunition, there is recent evidence in 2022 that some factory-loaded ammunition is skating by Quality Control as factories maximize their production to meet world demand. Two recurring names with this problem are US-made SIG and Fiocchi.


DETAILS
Excessively Long OAL
It is possible for handloaded or factory cartridges with excessive length to jam the bullet into the rifling and create an OOB event. Finding the correct OAL range for your 9mm reloads is covered in detail in THIS document.

Poor Taper Crimp
Improper taper crimp on handloaded cartridges can leave excessive flair on the case mouth, or distort the shape of the cartridge case to the extent that can create an OOB event. Adjusting the reloading dies to achieve proper Taper Crimp is covered in detail in THIS document.

Deeply Seated Bullets
Inside each cartridge case, the case wall must thicken to support the higher pressures experienced by the case head and physically mount the primer. It's important to understand there is no "standard" set of inside case dimensions; each case manufacturer builds to their own set of dimensions. An accurate depiction of the case wall thickening is shown below...



This case wall thickening is typically not a problem with 115gr and 124gr bullets, and users of these bullets rarely experience any problem. However when handloading the longer 135gr and 147gr bullets the user may be faced with a dilemma. Their chamber might require a shorter OAL to clear the chamber freebore, and this foreshortening of the OAL forces the base of the bullet deeper into the case where a bullet-to-case collision can occur. When the base of the bullet encounters the internal case wall ramp, the middle of the cartridge case is often imperceptibly budged outward. This is shown in the cartoon below...



This can usually be avoided by calculating the seating depth of the bullet, and then using the depth reading portion of a measuring caliper to check the internal clearances on your brand(s) of brass. As stated before, each case maker builds to a unique dimension and often this situation can be prevented by simply avoiding certain brands of brass. Gathering depth measurements on brass is shown below...



Also see: https://czfirearms.us/index.php?topic=111500.0

Expanded Case Heads
It is unusual for the detonation of gun powder inside a 9mm Luger cartridge case to expand the case head to such a degree that it does not return to it's normal maximum diameter of 0.391". However the growing popularity of "9 Major" in the Open Class of action pistol competitions means that if you harvest "range pickup brass" and your favorite range hosts these type competitions, then there is a very good chance that you will encounter this issue.

"9 Major" chamber pressures are extremely high; high enough to expand the thickest part of the brass case. With normal chamber pressures, re-sizing the brass case returns all the case dimensions to better-than-original condition and everything is fine. However, when expansion happens at the case head and rim, normal reloading dies cannot reach that area because of the shellplate, and so the overly large case is allowed to enter the ammunition stream. This type case head expansion is clearly shown in this photo...



Notice that there is no "guppy belly", no distorted primer, nor any other visible evidence of this case being irregular, except that it will not fit the cartridge gauge. For these reasons, this particular issue can be devilishly hard to spot before a jammed chamber event occurs.

NOTE: If "range brass" is your only source and/or expanded case heads seems to be a recurring issue, then the only guaranteed solution is a rolling style case resizer, which can accurately reshape the full-length of the tapered 9mm Luger case. See: https://www.rollsizer.com/


SUGGESTIONS
• The best medicine for each of these situations is prevention, through accurate measurements using good quality measuring tools, a cartridge gauge, and finally your gun's barrel. With these tools you can set up good processes to produce good, useable ammunition. The extent to which you implement process changes might range from less important for backyard target practice, all the way to very important for the serious competitor.

• Should you have this situation arise on the range, then immediately drop the mag. While tightly gripping the slide with one hand, hammer the rear of the pistol grip with the palm of the other. It will take several very powerful blows to hopefully dislodge the wedged-in cartridge. If/when the cartridge is extracted it is highly suggested that it be taken back to the reloading bench for a full fault analysis, so that your reloading process can be modified to prevent future reoccurrences.

• Should the extractor fail to withdraw the cartridge despite the slide moving to the rear, then it is very important that the powder and primer be de-activated before inserting a rod down the muzzle.

• Correctly sized cartridges (both factory or handloaded) should be able to pass the "Plunk and Spin" test. With your barrel removed from the gun, A) a properly-sized cartridge should be able to fall all the way into the chamber using only it's own weight and "head space" on the ledge at the end of the chamber. B) Once head spaced, the cartridge should be able to rotate freely back and forth. C) When the barrel is inverted, the cartridge should exit the chamber, again using only its own weight. Falling in and out demonstrates the correct case dimensions. Once head spaced, the ability to spin demonstrates a useable cartridge length (OAL). A proper "Plunk and Spin" test should be conducted on 5-8 cartridges in every box of 50.

• A great way to find an offending cartridge area is to cover the cartridge with marker ink, and then lightly rotate the offending cartridge inside the chamber. The ink will be rubbed off at the offending area of the cartridge.


Hope this helps.

[Wobbly]

Common Reloading Issues Related to 9mm Tapered Cartridges -
Loose Bullet Retention

It is quite common for reloaders to experience a phenomena in auto pistol cartridges known as "bullet setback", where the bullet is not tightly held in the case. In revolver cartridges there is a crimp cannelure and the mouth of the case is roll crimped into this notch in the bullet, holding it securely. But auto pistol bullets have no such cannelure, and so the bullet is held in place solely by the tension created when the case mouth inside diameter (ID) is smaller than the bullet's outside diameter (OD). This then creates a situation where the bullet is basically held in the case solely by a "press fit".

This is made possible by the "spring back" qualities of the brass. The larger bullet is pressed into the mouth of the smaller case, and the brass of the case mouth is elastic enough to shrink back around the bullet. This "press fit" is typically on the order of 0.002" difference between the 2 diameters.

• It is very important for the reloader to realize that the case mouth tension (aka 'case neck tension' in bottleneck rifle cases) that holds and retains the bullet in place is only the result of the difference in the 2 diameters BEFORE the bullet is inserted into the case.

Bullet retention cannot be added to or improved AFTER the bullet is inserted into the case. Therefore, taper crimp does not create or improve bullet-to-case retention. If fact, adding more taper crimp has been shown to actually reduce case mouth retention.

CORRECTION
Poor bullet retention may be caused by anything that upsets the very delicate balance between the bullet's OD and the case mouth's ID. The 2 most common causes are:

A. Case Mouth Too Large To correct loose bullet retention you first need to understand how reloading dies work. The Sizing Die (which only works against the outside of the cartridge case) first shrinks the outside of the cartridge case to a smaller dimension than needed. But, because of the tremendous variations in case wall thickness, the inside of the case mouth is not set to a precise ID.


A typical case Expander may be combined with other functions such as belling

Then in a traditional secondary operation, the case Expander (which works only on the inside of the case) reopens the case mouth to a precise inside diameter. It's this precise ID, working in together with the precision OD of the bullet, which then successfully holds the bullet in place.

If you are experiencing loose bullet retention, then the solution may be to reduce the diameter of the Expander in 0.001" steps until the proper retention is achieved. Reducing the Expander diameter is easily accomplished with 400 grit emery cloth while spinning the Expander in a drill motor.

B. Bullet Too Small Poorly made bullets can simply be undersized. This is more common with plated bullets, but can also happen with cast lead bullets. If your bullets are labeled as 0.355" (for instance), but actually measure at something smaller, then you have a bullet issue.

These are the 2 most common causes, but as with any abnormal occurrence, can have multiple causes. Close observation and careful measurements usually save the day.

TESTING
The reloader can (and should) randomly test pieces of their reloaded ammunition for this fault by holding the cartridge case and pushing the nose of the bullet into their reloading bench. With pressures under ~10 lbs, there should be no detectable movement of the bullet sliding back into the case, or "bullet setback".

OTHER FORMS
Bullet setback may also be experienced after a specific cartridge has been repeatedly loaded from the mag into the chamber by "slingshot-ing" the auto pistol slide. However, the forces of repeatedly loading the same cartridge over and over are so large that bullet setback is common in this instance, even on properly loaded factory auto pistol cartridges.

So although bullet setback might be noted in this situation, it indicates ammunition abuse and not poor loading technique.