Reloading .450 Bushmaster cartridges requires a die sequence built for the cartridge’s straight-wall case and headspacing requirements. The press supplies the force, but the die set controls sizing, case-mouth expansion, bullet seating and taper crimp.

We selected the RCBS 21604 three-die taper-crimp set for the die station in our .450 Bushmaster Loading Room. It keeps the sizing, expanding, seating and crimping operations connected to the actual rifle, case, bullet and current loading reference.

What problem does this die set solve?

A press alone cannot resize a .450 Bushmaster case, prepare the case mouth for the chosen bullet or apply the taper crimp required by the loading procedure. This cartridge-specific set supplies those tools without substituting generic .45-caliber dies for the correct .450 Bushmaster process.

What each die does

Steel sizing die: resizes the case and removes the spent primer. RCBS specifies case lubrication for this hardened-steel sizing die.
Expander die: expands the case to accept the bullet and applies the controlled mouth flare needed for bullet entry.
Taper-crimp seating die: seats the bullet and applies a taper crimp while preserving the cartridge’s proper headspacing relationship.

Why this matters for .450 Bushmaster

The .450 Bushmaster workflow must keep case dimensions, bullet selection, seating and taper crimp connected. The die set performs the mechanical operations; its instructions, current load data and the requirements of the actual rifle establish the correct adjustment and measurement.

Continue through the complete .450 Bushmaster reloading sequence for the press, case preparation, measurement, brass, bullet path, load data and chronograph stations surrounding the die work.

Specifications

Cartridge: .450 Bushmaster
Manufacturer: RCBS
Manufacturer number: 21604
Distributor item number: RC21604
UPC: 604544637922
Set type: Three-die taper-crimp set
Included operations: steel sizing and depriming, case-mouth expansion, bullet seating and taper crimp
Sizing die: hardened steel; case lubrication required
Shipping weight: 1.5000 pounds

This listing is for the die set described above. Press, shellholder, cases, bullets and other loading equipment are sold separately unless expressly stated. Follow current RCBS instructions and complete, source-attributed load data for the exact components and rifle being used.

taper-crimp die set

RCBS .450 Bushmaster 3-Die Set — Sizing, Expanding, Seating and Taper Crimp