This buffer and spring will not work. You do not necessarily need a heavier buffer though. Calibers like the 450 bushmaster are generally designed to work with standard 3oz buffers. You could use an H1/H2 buffer and that would run fine. But you don't need something extremely heavy to get the job done. I will link an H1/H2 buffer that will work fine with your build below.
https://www.opticsplanet.com/aero-precision-ar15-buffer.html