Basics of Case Sizing — How To Set Up and Use Sizing Dies

This article is part of Sinclair Int’l Step-By-Step Reloading Series. Most of the products mentioned in this article are sold through Brownells.com.

by Roy Hill, Brownells/Sinclair Copywriter
Making your own precision handloads is a meticulous journey with many steps, many important matters to consider, and many sets of measurements to calculate. For those who pursue the perfect group, the highest score, the really long accurate shot, the rewards more than outweigh the effort. Choosing the right cases, deburring the flash holes, making the primer pockets uniform, trimming the cases, and lubricating them are all familiar – and critical – steps along the journey. And now that your brass preparation is complete, you are at last ready to start running the cases through your press and fill them with primers, powder, and bullets. The very first die the brass encounters is the sizing die. You insert the case, work the press’s lever to return the case to its correct pre-fired dimensions – and the journey continues.

There are three types of sizing dies to think about: neck, full-length, and small base. All three have specific benefits and potential drawbacks, and you should choose the type of die you use by thinking very carefully about what kind of shooting you plan to do with your handloads. No matter which type you select, most sizing dies will also punch out the old spent primer with some sort of decapper assembly that uses a hardened steel rod. Many types of sizing dies use an expander ball inside the die to make sure the neck of the case will accommodate a bullet after being sized. With some size dies, the expanders are easily removable and interchangeable, letting you get exactly the neck tension you want. When sizing cases (neck of full-length), rifle cases always need lube.

Neck-Sizing Dies
Neck-sizing dies resize only the neck of the case. The benefit of sizing only the neck is that the brass is “worked” very little, reducing the amount of changes to the brss. [We recommend full-length sizing for all applications after the first couple of firings, and semi-auto brass should be full-length sized every time!] Sinclair recommends that neck-sized-only cartridges should not be used any in other rifle besides the one they were originally fired from [unless they are also FL-sized], or in any action other than a bolt-action.

Full-Length Sizing Dies
Full-length sizing dies resize the full length of the case, not just the neck. Full-length sizing helps create handloads that will function in any rifle, not just the one from which the cases were originally fired. The potential downside of full-length sizing is that it may shorten case life because it works the brass more than neck sizing. But it’s possible to “tune” today’s full-length sizing dies so they barely work the brass at all, as this article by Sinclair Reloading Tech Ron Dague shows.

Illustration Shows How a Full-Length Sizing Die Works

Another way to reap the benefits of full-length sizing is to use Redding’s full-length bushing dies, which size the full length of the case but use a system of interchangeable bushings that enable you give the case neck the bare minimum of resizing needed. To see how finely adjustable bushing dies are, and how they resize the case while fully supported, CLICK HERE for Video. The neck bushing helps you precisely control the neck tension to help increase the consistency and accuracy of your handloads.

Small Base Dies
A Small Base Die is another type of full-length sizing die, but one that is typically used when reloading for semi-automatic rifles, like the AR-15, M14, or AR-style .308 rifles. (It may also work well for bolt guns that need extra sizing on the lower section of the case.) A small base die works exactly like a full-length sizing die, only it compresses the brass just a bit more, usually about .001″ more, and may even push the case shoulder back just a hair. Small base dies give that extra bit of compression to the brass to help make sure the case will properly extract from a semi-automatic firearm. The upside is that you get handloads that should work flawlessly in your semi-automatic. The downside is case life may be shortened as compared to brass used only in one bolt-action rifle, because the brass is worked more.

Shoulder Bump Gauges
A handy tool for setting up your full-length sizing dies as close as possible to your rifle’s chamber is a shoulder bump gauge. The bump gauge lets you resize the case as little as possible, to extend case life and help your handloads fit your rifle almost like a neck-sized only die. You use deprimed cases fired in your rifle and bump gauge inserts to help you set up the die so it resizes the case only about .001″ to .004″, depending on what type of rifle you’re shooting.

Video shows how to use a shoulder bump gauge to set up your full-length dies

Similar Posts:

• SIZING DIES: Full-Length Dies, Neck-Sizing Dies, Small Base Dies
• DIE BASICS: Full-Length Dies, Neck-Sizing Dies, Small Base Dies
• Intro to Full-Length Dies, Neck-Sizing Dies, and Small Base Dies
• How to Set Up Full-Length Sizing Dies and Control Shoulder Bump
• Full-Length Sizing Die Set-Up — Tip from Sinclair International

Tags: Bushing Dies, FL Sizing Die, Full Length Die, Neck Sizing, Sinclair Int'l, Small Base Dies