The Redding Precision Expanding Die with 0.2830" Expanding Mandrel (MPN 21541) is a dedicated reloading tool engineered to expand cartridge case necks from the inside out after full-length resizing or neck sizing. Machined from CNC, heat-treated steel with hardened tool-steel mandrels, this die features engineered angled alignment surfaces that maintain concentricity between the mandrel and the case neck. By setting an exact internal neck diameter calibrated 0.0010" under the standard 7mm bullet diameter (.284"), it delivers consistent neck tension of approximately 0.001" to 0.002" while minimising seated bullet runout.

Key Features

• Precision Neck Expansion: Expands downsized case necks internally using a 0.2830" tool-steel mandrel to deliver consistent bullet release and lower neck runout.
• Self-Centring Alignment: Angled internal mating surfaces align the expanding mandrel concentrically with the case neck during the press stroke.
• Universal Press Threading: Built with standard 7/8"-14 threads for compatibility with standard single-stage, turret, and progressive reloading presses.
• Modular Mandrel System: The die body accepts interchangeable Redding expanding mandrels, which are available in 0.0005" increments.

Specifications

• Manufacturer Part Number (MPN): 21541
• Calibre Compatibility: 7mm / .284 calibre cartridge cases
• Mandrel Diameter: 0.2830" (machined from hardened, precision-ground tool steel)
• Thread Interface: Standard 7/8"-14 reloading die threads
• Die Body Construction: CNC-machined, heat-treated steel
• Operation: Manual, mechanical benchtop reloading press required

Who is the Redding Precision Expanding Die W/0.2830 Expanding Mandrel for?

• Long-Range Precision Rifle Reloaders — relies on this reloading neck expanding die to achieve consistent 0.001" to 0.002" neck tension on 7mm brass using the precision-ground 0.2830" mandrel to minimise bullet seating eccentricity.
• F-Class, PRS, and Benchrest Competitors — integrates this expanding die into their brass prep workflow via standard 7/8"-14 press threads to eliminate internal case neck variations after sizing.
• Precision 7mm Hunters — uses the 0.2830" expanding mandrel in this die to standardise bullet grip on resized .284-calibre hunting cases without overworking the case neck brass.

Less suitable for: Reloaders seeking heavy neck retention for rough-feeding semi-automatic actions, or those needing to expand brass without prior sizing; standard full-length sizing dies with conventional expander balls or smaller 0.2810"–0.2825" mandrels fit high-retention applications better.