Find the missing numbers ($A$ & $B$) in the series and find the value of $B-A$:\n
$$123,148,A,198,223,B,273$$

Let's determine the common difference by checking the known consecutive terms:
$$148-123=25$$

$$223-198=25$$

Since the series increases by a constant addition of $+25$:

$$A=148+25=173$$

$$B=223+25=248$$

Now, we calculate the value of $B-A$:

$$B-A=248-173=75$$