I could not find much data on this subject, but I found about 22 numbers, spread out over a few years, so not 100% reliable here. But, on some analysis, it appears that the average offset to add to the BarBri raw score is about 37 points. Also, no one in this data set scored less on the actual MBE in comparison to BarBri's simulated exam, so a conclusion could be that the actual exam is, therefore, less difficult. So if you scored a 100/200 on the BarBri Simulated MBE, then you may predict that you will have an MBE score of 137 (actual). Series 1, in blue, represents BarBri's simulated exam, and Series 2, in orange, represents the actual MBE score.
About the MBE, it consists of 200 questions, and you have 6 hours to finish the exam. Exam-takers receive three hours during the morning session to complete the first 100 questions, and another three hours during the afternoon session to complete the second 100 questions. Only approximately 175 questions on the exam are graded, the other 25 are experimental questions. The score, however, will be normalized to range between 0 and 200.
States have different thresholds for determining a passing score, e.g., DC requires a combined score of 266. The total UBE exam comprises a performance examination (e.g., 2 written assignments), 6 essays on various UBE subjects, and the MBE. The MBE is weighted 50%.
So my guess is that 50% for UBE, 20% for the Performance Exam, 30% for the Essays.
Example
UBE score (50%): 167
Performance Exam (PE) (20%): 140
Essays (30%): 140
The score would be, 167 + (120*0.4 + 140*0.6) = 299
Note that a 167 on the MBE with 100 on both PEs and Essays would result in a 267, a pass.