As you have probably seen by now, and if I understand how it works, the actual values in a scale have no real bearing on the calculates values. The first digit in the scale has a value of 0 no matter that you enter. The second is 1 etc.... This because Moodle sees the ordinal value of the digit and not its cardinal value. It has a lot to do with arrays (but no more on that.).
The only way you can create a scale, for 250 points would be to enter all 250 numbers into a scale and it would be tedious at best to have to scroll through the list to place a grade. More so, you still cannot issue a 0 as it will show up as 1 point.
I don't believe in the % grading anyway so I issue points. A full semester can accumulate 2145 points for an A and fewer for B, C, and my scales reflect this so I can issue points from the look up when grading. Granted, it would be nice if I could enter a grade instead but I live with this.
This is why I totally ignore the calculations and have a different way of grading. I use points and explanation is not all that easy to implement in Moodle. I use a different method to populate a scale.
A typical scale for me contains:
NA, 0, 1, 12, 45, 74, 89, 104, 128, 137, 160, 1, NA
(For this example, ignore the values lost between numbers. This is just an example.
A grade of 89 will give the system a grade of 7 which it totally useless and a grade of 113 is not possible here.)
In this idea, when you grade a project, you give the number of points that you choose from the list. NA is useful if you have an entry that to which a grade does not apply. I always include the 1 for a project that was handed in but cannot be evaluated. The 1 and NA at both ends are useful so you don't have to scroll to the value if it is a long list of numbers.
With this method, of course, you will lose all the value of automated calculation and spontaneous indication of present grade. For me this is not a problem. I grade by extracting the values to Excel and do a simple cross summation of points and then use a curve to evaluate their work and issue a letter grade. My logic is that there are few, if any, places in the real world where you will be evaluated by a percentage.
After some understanding, and argument to prevent any change in the old fashioned K-12 grading system, the students prefer my technique.
Granted, all this is a bit wordy but it has worked for me for 10 years now. Maybe someday, Moodle will evolve beyond of the percent grading system and allow a point-value method.