The RCBS 300 Rem Ultra Mag Neck Sizer 2-Die Set (Manufacturer Part Number 17602, also referred to in Australia as R17602) is a specialized reloading tool designed for precision handloaders targeting maximum accuracy and extended brass life. This mechanical set is engineered to resize only the neck of previously fired .300 Remington Ultra Magnum (.300 RUM) cartridge cases. By leaving the fire-formed body and shoulder of the brass untouched, the cartridge maintains an exact, custom fit to the rifle chamber from which it was fired. This results in highly uniform chambering and consistent shot-to-shot accuracy.

Key Features:

• Targeted Neck Sizing: Resizes only the neck of the case to securely hold a new bullet, leaving the fire-formed cartridge body and shoulder dimensionally unaltered.
• Extended Case Life: Prevents the over-working and stretching of brass, which dramatically increases the reuse cycle of expensive .300 RUM cases.
• Integrated Expander-Decapping: Sizer die features a hardened decapping pin and expander ball to deprime and size the neck in a single manual stroke.
• Complete 2-Die Set: Includes one Neck Sizer Die with an expander-decapping assembly and one Regular Bullet Seating Die with an adjustable seating plug.
• Durable Construction: Manufactured from case-hardened, proprietary tool steel.

Specifications:

• Compatible Calibre: .300 Remington Ultra Magnum (.300 RUM)
• Thread Interface: Standard 7/8"-14 thread
• Product Weight: Approximately 544 grams
• Material: Case-hardened steel
• Required Accessories: RCBS Shell Holder #38 (sold separately)

Who is the Rcbs 300 Rem Ultra Mag Neck Die Set for?

• Precision long-range handloaders — who require maximum shot-to-shot uniformity for bolt-action rifles, utilizing this 544-gram neck sizing reloading die set to maintain a precise, fire-formed fit to a single rifle chamber.
• Handloaders seeking to maximize 300 RUM brass life — who want to extend the utility of expensive casings by using a neck sizing reloading die set that avoids the structural stress of full-body resizing on a standard 7/8"-14 thread press.

Less suitable for: semi-automatic, lever-action, or pump-action firearms where neck-sized ammunition lacks the physical clearance needed for reliable chamber feeding, or for cartridges that have exceeded 4 to 5 firings and exhibit chambering resistance, which instead require a full-length sizer die to restore original factory dimensions.