Case expansion is critical when loading pistol ammunition. Too little case mouth expansion, and you’ll fail to place/retain bullets, and you’ll also shave the bullet if you’re loading hard cast lead bullets. Too much case mouth expansion, and you’ll over-work the brass and cause it to fail prematurely. So let’s take a look at some popular case expander dies, talk about how to setup such a die, and then evaluate and measure case mouth expansion.

Comparison of Expander Dies

There are several types of expander dies on the market today, each with different pros/cons as well as different capabilities. Here are some of the popular expander dies on the market today:

From left we have: (all for 45 ACP)

1. LEE expander die (combination powder-through die and dedicated expander depending on how it’s configured)
2. Hornady expander die
3. RCBS expander die
4. Lyman expander die

There are some subtle differences between the various expander dies on the market, but one of the important differences is the expander plug profile. There are two popular types of profiles:

1. Single step: A conical or curved profile that puts a single feature on the case mouth (a flare or bell).
2. Multi-step: A design that features a straight section (for placing bullets with a press fit) and a conical or curved section to flare the case mouth.

The Lyman expander shown above is a good example of the multi-step expander profile (as shown in video). The advantage of a multi-step design is namely bullet placement and retention. With 1/16″ of [very slight] press fit (using Lyman for example) the bullets will stay in the cases even when a progressive press is indexing. This retention is also important if you’re placing/removing cases from a loading block.

Verifying Expander Die Setup

The key measurement used to validate expander die setup is the enlargement of the case mouth. This measurement is is easy to perform using digital calipers (I use the iGaging OriginCal 0-6″ calipers).

Step 1: Get measurement of case body (not expanded portion)

Step 2: Zero the calipers

Step 3: Measure the case mouth – indicated value is measurement of expansion

It’s that easy. How do you decide “hot much is enough”? Generally you’ll want about .005″ – .010″ for non-lead bullets, and .010″ – .020″ for lead bullets.

These measurement guidelines (dimensions) are only rough guidelines. You really want to use *as little as possible* case mouth expansion, while satisfying the following:

1. Bullets stay placed in case through your loading process.
2. There is no shaving of lead or copper when seating bullets.

So I would recommend that you start with the dimensions given as a starting point, and adjust to as little as possible expansion while reading the verifying the criteria above. That’s it!

Do you have a favorite expander die, or a tip/trick for setting up these dies? Please leave a comment!

Thanks,
Gavin