Sizing Dies and Crimping

Sizing dies can be divided into two main groups: full-length sizing dies and neck sizing dies. In this reloading school, we use dies that offer full-length sizing.

A perennial topic among reloaders is the debate between full-length and neck sizing. Previously, neck sizing was considered the best way to crimp, resulting in less stress on the case. Some believe that the swollen dimensions of the case from neck sizing offer better accuracy than full-length-sized cases. This is outdated information by today's standards. The most successful benchrest shooters and other enthusiasts of precise firearm operation have long been using full-length sizing. Full-length sizing is the only sensible way to crimp cases in hunting applications.

Full-length sizing can be understood in two different ways. One is uncontrolled "oversizing," where the case is crimped without a precise definition of the case-to-chamber fit. In the other method we are focusing on now, the degree of sizing is determined precisely, meaning the case-to-chamber fit is determined when adjusting the sizing die.

Depending on the type of die, one or two different events occur in the sizing die. In traditional dies, the case is sized entirely, after which, during the extraction phase, the mouth of the case is opened by the opening part of the firing pin on the die's mandrel. This type of crimping thus modifies the case in two directions from its neck. First, the die oversizes the neck, and then the opening part of the mandrel opens it to the correct size. On the other hand, more modern dies only contract the case from one direction. These dies use a replaceable neck ring, or bushing, on the neck section. When using this type of die, the opening part of the decapper is replaced with one that does not touch the case mouth during extraction.

When choosing between a traditional sizing die and a bushing die, it is worth remembering that precise cartridge loading does not necessarily require using a modern bushing die. Instead, the choice of die can affect the case's lifespan, especially regarding the neck. The neck is under particular stress with traditional dies because, especially when using a CIP-length chamber, it first expands significantly oversized, after which the sizing die contracts it significantly undersized. Then, the mouth of the case is expanded again to fit the bullet when the case is extracted from the die. Thus, the stress on the case neck is greater with traditional sizing dies.

When choosing a sizing die, common sense should be used. If there is more natural rotation in a batch of cases than rotation related to the case's lifespan, thinking about reloading cycles is unnecessary. For example, in normal hunting loads, cases are lost, whereas in target shooting, they can be carefully collected. Determining reloading cycles in hunting loads is also a challenge, whereas maintaining case rotation is easy in target shooting.

Sizing Die Structure and Adjustment

Adjusting a sizing die is relatively straightforward. The first step in adjustment is to install the decapper at the correct rough depth. In this task, it is sufficient that the decapper protrudes just enough over the base of the case holder. In other words, when the cartridge is pressed into the sizing die, the length of the decapper should be enough to eject the fired primer from the case. It's important not to exaggerate, as the length of the decapper is limited, and the pin must not bottom out inside the case holder. An excellent way to adjust the decapper is to remove the case holder from the press and place it against the mouth of the die. When the decapper protrudes over the base of the case holder by about a millimeter, the decapper is installed at the correct depth.

​In bushing dies, adjusting the decapper occurs by changing the internal length of the decapping rod, as the locking nut's task is to hold the neck ring in place. Otherwise, the adjustment is made just like in basic dies. However, the most crucial thing in bushing dies is choosing the appropriate neck ring for use, measured from the neck of a loaded cartridge. The outer diameter of the neck is measured and converted to inches if necessary. The measurement is taken with a thousandth of an inch accuracy, after which three thousandths of an inch is subtracted from this number. Then, in addition to the die, neck rings of the corresponding diameter are obtained, preferably with a couple of extra rings - one tighter and one looser. In other words, it's advisable to acquire a standard bushing die with three neck rings, with a range of .002" - .004" subtracted from the outer diameter of the neck.

​When using bushing dies, it's important to remember that the necks of cases from different manufacturers have different wall thicknesses, which significantly affect the diameter of the neck ring used. In this sense, traditional dies are recommended if various cases are in use and straightforward crimping is desired. However, if case batches are well controlled, bushing dies provide additional lifespan.

Adjusting the degree of sizing

Adjusting a full-length bushing is done gradually and by trial and error with cartridges fired from your rifle to achieve the desired result. Typically, manufacturers' basic bushings are slightly oversized, so it's essential not to contract them more than necessary.

​In the initial setup, the sizing die is placed in the press as follows:

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• Press the handle of the reloading press down, causing the case holder to rise to its upper position (note that in some presses, the upper dead center is slightly before the handle's extreme position).

• Screw the sizing die into the case holder until it is fully tightened, then

• Open the sizing die by one full turn,

• Ensure that the decapper reaches the depth to eject the primer from the case in this position (i.e., the tip of the decapper passes the base of the case holder).

This is the starting adjustment for the sizing die, from which the depth adjustment begins.

Before starting the sizing die adjustment, the firing pin with its spring is removed from the rifle's bolt. This provides the best feel of the bolt, as the force required to cock the firing pin does not interfere with the bolt's movement. The rifle bolt moves smoothly, and only the resistance caused by the case in the chamber is felt when closing the bolt.

The first sizing of the case is done with the sizing die adjusted to one full turn open. The case needs to be thoroughly lubricated but not too thickly, and the inside of the case neck needs to be lubricated when using basic bushings. Then, the case is fitted in the rifle chamber. At this point, there should be resistance when closing the bolt. From this point on, the sizing die is adjusted by tightening it by one-eighth turn at a time. Typically, the die needs to be fully tightened before the desired degree of sizing is achieved.

When adjusting the suitable degree of sizing, it's typical for the force required to close the bolt to decrease steadily until slightly before the desired degree of sizing, the stiffness increases. This is because the space for the case sizing in the die decreases, and the brass of the case moves where it can within the sleeve. This is usually a sign that the desired degree of sizing is close. From this point on, the tightening of the die between sizings is halved, meaning the die is tightened by 1/16 turn at a time.

The die adjustment is stopped when the degree of sizing is so close to the desired level that only a slight resistance is felt when closing the bolt. At this point, the sized case is replaced with an unsized one, and the feel in the rifle chamber is tested. Usually, the resized case chambers smoothly without issues, indicating that the die is correctly adjusted. When gradually increasing the sizing, the case undergoes slightly less deformation than with a single sizing. After this, the sizing die is locked into the press with a locking ring, and the locking ring is tightened onto the die. The sizing is adjusted.

Measuring between the fired and resized case?

There is often discussion about how the headspace between a fired case (a case in the dimensions of the cartridge chamber) and a resized case relates to each other after the sizing die is adjusted. This question is primarily academic in cases where the sizing die is off-the-shelf merchandise. In such cases, the sizing degree must be determined as described above, and measurement has no practical significance. Measurement comes into play when the sizing die is specifically made for a particular cartridge chamber and is in the correct dimensions.

CIP-specified firearms and their cartridge chambers have tolerances within which the cartridge chamber is dimensioned. Most often, cartridge chambers fall between the definitions of minimum and maximum, and only very few manufacturers produce their firearms' cartridge chambers to, for example, the CIP minimum. Thus, there can be quite a variation in cartridge chamber dimensions, even if it's the "same caliber." From the reloader's perspective, each firearm is an individual with its own caliber. At the other end of the equation is the cartridge case neck bushing manufacturer, who makes bushings so that they can contract cases fired in cartridge chambers dimensioned to CIP or SAAMI minimums. This is why mass-produced sizing dies are always more or less oversizing. Therefore, it's essential that the die is adjusted correctly and only sizes enough to allow the cartridge to chamber smoothly, without excessive modification. With almost any die, it's possible to make excessive sizing.

Discussions about the headspace between a resized case and the cartridge chamber often revolve around extreme users, represented worldwide by benchrest shooters. Regarding benchrest rifles and their reloading equipment, it's worth remembering that they belong to a group of firearms where, for example, the caliber designation is only superficial. Cartridge chamber dimensions are often based on the dimensions of the case used, and reamers for sizing dies are typically ordered from the same manufacturer as the rifle's cartridge-chamber reamer. In this case, it's a system where every component is in perfect balance with each other. These are firearms where every detail has been thoroughly considered. This is far from what factory-produced firearms and the cartridges used in them are capable of, so the same rules cannot be directly applied to factory firearms and reloading associated with them.

Why Full-Length Resizing?

Let's briefly revisit the debate between full-length resizing and neck resizing. It's common in comparing these two different resizing methods that the pursuit of neck resizing is alive and well among reloaders. There's a reason for this: neck resizing was the prevailing method in precision shooting circles just a few decades ago. However, the weakness of neck resizing is that the case brass changes with each shot, so its interaction with the cartridge chamber also changes. This adds a variable to the inconsistent reloading process, which changes slightly with each reloading session.

When neck resizing is used, the force required to chamber the case increases at some point to the extent that the case requires full-length resizing. This starts the cycle anew. In other words, when neck resizing is used, the case constantly changes, which is easily noticeable in the firearm's precision.​

Neck resizing also has practical problems in shooting situations. In benchrest shooting, neck resizing has disappeared partly because between shooting sessions, either a too hot load (making bolt opening difficult) or a cartridge that chambers too tightly pose a potential risk to the firearm's movement on the rest. The same problem is also emphasized in shooting from the prone position, where the movement of the bolt should always be as smooth as possible so that the loading of the firearm itself does not interfere with precise operation.

About Lubrication

Lubricating the case is essential during resizing to ensure smooth movement in and out of the resizing die. In the past, it was typical to use oiling pads, and various substances, including motor oil, were used for lubricating cases. Nowadays, lubricants are broadly divided into sprayable lanolin-based lubricants or waxes, which are applied to the case surface by hand. When loading large quantities, lubricating with sprayable substances (such as Dillon D-C-L) is most straightforward, while using waxes is convenient for small batches.

Especially when using traditional resizing dies, it's crucial to ensure lubrication not only on the outside of the case but also on the inside of the case neck. This is most easily done with wax, which can be applied to the inside of the case neck with fingers. This facilitates the work of the case mouth expander. This is important not only for smooth loading but also to prevent stretching the case mouth outward during extraction. In addition to lubrication, it's advisable to brush the case necks before resizing, for example, with a brass brush, to reduce resistance during neck expansion.

It's important to use a reasonable amount of lubricant. Excessive lubricant can cause slight inward bulges at the case shoulder, although this is primarily a cosmetic issue. Similarly, especially when using case waxes, care should be taken to clean the inside of the resizing dies regularly from wax residues, as these tend to accumulate on the inner surfaces of the dies, where they can cause problems.

Good lubrication has a significant beneficial effect on the loading process and helps avoid unpleasant issues. If lubrication is insufficient, some calibers tend to stick easily in the resizing die. Also, the decapper sticking into the case neck may lead to its unlocking failure, causing the decapping rod to slide out of the die during extraction.

After Resizing

Resizing requires lubrication, and lubricant residues, in turn, can hinder other reloading aspects. For example, oil trapped inside the case effectively dampens the ignition of the primer and powder, so all excess oil must be removed from inside the case. Therefore, moderation in lubricating the case neck is advisable, as this lubricant residue is the most difficult to remove. This is also a good reason to exclude actual oils from the resizing process.

​Wiping the cases clean of lubricant residues is necessary because lubricated and dry cases behave differently when fired. A dry-case surface provides an accurate indication, for instance, of the pressure level of the load. Lubricant residues on the case surface often manifest as gas blow-by between the case and the chamber. The easiest way to remove lubricant residues is to clean the cases after resizing, for example, with a rag dampened with brake cleaner.

​Foundation

Much emphasis is placed on powder charges and raw data concerning loads in reloading discussions. Still, the role of case resizing in the reloading process often receives far too little attention. However, resizing is a crucial part of the foundation on which reloading is built and must be done before further discussion. An appropriately resized case is the cornerstone of reloading.