At 50A: ADC=2987, offset=485. (2987-485) * 20 = 50040mA (50.04A)
At 4.24A: ADC=700, offset=485. (700-485) * 20 = 4300mA (4.3A)
At 1A: ADC=534, offset=485. (534-485) * 20 = 980mA (0.98A)

Not perfect. However, there are some things that doesn't quite add up here... You should be getting 60mV per A so at 50A you should get 3V or a count of 2457+offset. Now, you say that the offset is 485 which should give you a total of 2942 at 50A, yet you say that you get 2987 but never mind.

In theory, provided that your VRef is exactly 5.000V you will get 49.152 'counts' per A. If you get yoursefl a voltage reference of 4.096V then your ADC will report the measured voltage in units of 1mV instead which means that you'll get 60 counts per A - might make it easier for you.

/Henrik.