The Redding 300 Win Mag Neck Sizing Die (Part #81153) is a precision reloading tool designed specifically for bottleneck .300 Winchester Magnum cartridge cases firing standard .308" diameter bullets. Machined from alloy steel on Hardinge super-precision lathes, heat-treated in atmospherically controlled furnaces, and hand-polished, this die resizes only the case neck while preserving the fire-formed dimensions of the case body and shoulder. By eliminating unnecessary working of the brass at the shoulder and web, it extends cartridge case life and maintains concentric chamber alignment. It mounts via standard 7/8"-14 threads and includes an internal decapping rod assembly with an expander ball (Part #40307) to deprime cases during the sizing stroke.

Key Features

• Targeted Neck Resizing: Sizes only the neck portion of .300 Win Mag brass, leaving the fire-formed body and shoulder intact to preserve exact chamber fit.
• Extended Case Longevity: Minimises brass fatigue, work-hardening, and stretching, reducing case trimming frequency and prolonging usable brass life.
• Integrated Decapping Assembly: Deprimes spent primers and sets internal neck tension using an integrated expander ball and decapping pin during the sizing stroke.
• Super-Precision Machining: Turned from solid alloy steel on precision lathes and hand-polished to ensure smooth operation and consistent dimensions.
• Standard Press Mounting: Uses industry-standard 7/8"-14 threads for compatibility with standard single-stage and turret reloading presses.

Specifications

• Calibre: .300 Winchester Magnum (.300 Win Mag)
• Bullet Diameter Compatibility: .308"
• Mounting Thread: 7/8"-14
• Material: Heat-treated, hand-polished alloy steel
• Internal Assembly: Decapping rod with expander ball (Part #40307) and decapping pin
• Operation: Manual, mechanical reloading tool
• Required Shellholder: #6 shellholder (such as Redding Part #11006)

Who is the Redding 300 Win Mag Neck Sizing Die for?

• Bolt-action rifle reloaders seeking maximum case life and accuracy — who require a 300 Win Mag neck sizing die with standard 7/8"-14 threads to size only the neck for standard .308" diameter projectiles, maintaining fire-formed chamber concentricity while reducing brass stretching.
• Long-range hunters firing brass exclusively through a single specific firearm — who utilise this 300 Win Mag neck sizing die to prepare cases loaded with .308" diameter bullets for the exact same bolt-action rifle, ensuring minimal working of the brass and consistent neck tension across reloading cycles.

Less suitable for: Semi-automatic, lever-action, or pump-action rifles that require full-length resizing to ensure reliable feeding and extraction; sharing fired cartridge cases across multiple different rifles; or cases showing chambering resistance due to body and shoulder growth after 3 to 5 firing cycles. In these situations, a full-length sizing die or dedicated body die suits better.