Robert, Interesting question. This 450 Bushmaster round will fit and function in a 450 Bushmaster rifle. Here are the specifications-----------------bullet diameter .452 in (11.5 mm)
Neck diameter .4800 in (12.19 mm)[1]
Base diameter .5000 in (12.70 mm)[1]
Rim diameter .473 in (12.0 mm)[1]
Rim thickness .054 in (1.4 mm)[1]
Case length 1.700 in (43.2 mm)[1]
Overall length 2.260 in (57.4 mm)[1]
Maximum pressure (SAAMI) 38,500 psi (265 MPa)

Robert, if you mean the actual size of the projectile (bullet) Hornady Customer Service can answer this at Phone: 1-800-338-3220 ----------- hornady.com/bullets/rifle/45-cal-452-250-gr-ftx-450-bushmaster#!/#dealer-map