The Redding 0.3065 Expanding Mandrel (MPN: 21544) is a dedicated case-preparation component engineered for precision .30 calibre cartridge reloading. Machined from hardened, heat-treated tool steel and ground to final tolerances, this mandrel sizes cartridge necks outward from the inside. This expansion method prevents the case neck runout frequently caused by traditional expander balls and establishes uniform seating resistance across brass batches. It integrates directly into the Redding Precision Expanding Die Body via an angled, self-centring interface designed to maintain coaxial alignment on standard 7/8"-14 reloading presses.

Key Features

• Internal Neck Expansion: Expands case necks from the inside out, reducing bullet seating force variation and maintaining concentricity across repeated firings.
• Precise Diameter: Features a calibrated working outer diameter of 0.3065 inches, creating a controlled 0.0015-inch interference fit with standard 0.308-inch bullets.
• Self-Centring Alignment: Mates with the angled internal seat of the Redding Precision Expanding Die Body to eliminate off-axis tilt during the press stroke.
• Hardened Tool Steel Construction: Precision-ground and heat-treated to resist surface wear and galling over high-volume reloading cycles.

Specifications

• Manufacturer Part Number (MPN): 21544
• Calibre Compatibility: .30 Calibre (.308 Winchester, .300 Win Mag, .30-06 Springfield, 300 WSM, 300 PRC)
• Outer Working Diameter: 0.3065 inches
• Resulting Neck Tension: 0.0015 inches (nominal, with .308" diameter projectiles)
• Material: Heat-treated, precision-ground tool steel
• Required Tooling: Redding Precision Expanding Die Body (uses standard 7/8"-14 press threads)

Who is the Redding 0.3065 Expanding Mandrel for?

• Precision rifle competitors shooting .308 Winchester or .300 Winchester Magnum — sets a uniform 0.0015-inch nominal neck tension on .30 calibre brass using a 0.3065-inch diameter mandrel, delivering consistent bullet release force and lower velocity spreads across long strings of fire.
• Handloaders seeking to eliminate case neck runout during reloading — expands case necks outward to an exact 0.3065-inch internal diameter without dragging an expander ball upward through the case neck, preserving case concentricity during the sizing stage.

Less suitable for: Handloaders sizing cartridges outside of .30 calibre or running brass with an internal neck diameter already at or exceeding 0.3065 inches; cartridges of alternative calibres (such as 6.5mm, 7mm, or .338) require calibre-specific expanding mandrels, while reloaders seeking tighter bullet hold (0.002 to 0.003 inches) require smaller 0.3060-inch or 0.3050-inch mandrels.