Yes, the Luth-AR .223 Rifle Buffer Tube Assembly should work with a 450 Bushmaster with the appropriate gas system. However, I would recommend a heavier buffer system like the Aero Precision Enhanced Carbine Buffer Kit, the H2 or H3 model. You can find that kit here:
https://www.opticsplanet.com/aero-precision-enhanced-carbine-buffer-kit.html?_iv_code=29D-BFA-APAR15ECBK-APRH101242