How hot are fuses supposed to get / what kind of voltage drop is expected?

I built a system which should allow 300A discharging (1C) / 150A charging (1/2C)

But if I run more than 60A, my main battery fuse gets hot. If I run 300A the fuse get rapidly gets too hot to touch, and the heat spreads through to the attached cables, the battery, and the temperature sensor on the positive battery post. Is this somehow normal?? I’ve tried three different types of fuses with no real improvement.

— Here’s a photo of my installation with voltage drops labeled at 60 amps draw only. I don’t have voltage drops measured for the 300A draw because I don’t want to leave it running that way for long.

The main fuse on the battery is a 400A ANL fuse. I’ve tried with a 300A MRBF fuse and with two 150A MRBF fuses in parallel. All of them get hot to the touch when drawing over 60A.

Help?