A conventional mandrel die only holds the mandrel and expands the neck. This die is cartridge-family specific and also gives the case base a light sizing “touch” at the same time.

No. It is not a small base die. The base sizing is the same dimension as a full-length sizing die.

Yes. Sizing the base helps keep older brass from creeping oversized at the rear, which can reduce the likelihood of clickers over time.

As brass ages, the base can grow and become tight in the chamber. After firing, the rear of the case may not spring back enough. When opening the bolt, you feel resistance until it releases and “clicks.”

Basic setup:

1) Bring the ram all the way up.
2) Screw the die down until it touches the shell holder.
3) Tighten the set screws on the locking ring.

The ring has two set screws 90° apart so you should always have access to at least one.

The flat side is the “true” side (machined square to the threads on the same setup). Depending on your press type, you may flip the ring orientation for proper locking.

Use a 3/16" punch in the ring holes to snug it down when a wrench can’t easily reach.

These dies are cartridge-family specific. Derived cartridges generally use the same die body — you simply change the mandrel as needed.

Examples covered in the video:

• 6.5 PRC family: 6.5 PRC and common derivatives
• .284 family: .284 Win and common derivatives
• .308 family: .308 Win, 7-08, .260, .243, 6.5 Creedmoor
• 6BR family: 6BR, BRA, BRX, Dasher and similar derivatives

Possibly. Depending on how tight your brass is and how many firings it has, you may need some lube. Use lube as needed based on feel.

Yes. If you already have 21st Century mandrels and you’re happy with them, there’s no need to replace them.

Our mandrels are typically 0.002" under bullet diameter. We also offer sizes up and down in 0.001" increments and some options in 0.0005" increments.

Yes — they are coated with Armaloid for improved lubricity and surface hardness.

Yes — adapters are planned that allow you to use a brush in-press so you can clean necks by operating the press handle (especially useful on progressive setups).