I have been looking around the web without any conclusion.
The 5" 5906 PPCs that I have seen all have straight slide serrations.
The 6" 5906 PPCs that I have seen all have scalloped slide serrations.
Now all the 5" guns had serial numbers lower that the lowest 6" guns that I have seen.
So here is the question . . . . Have these always been different on the two slide lengths? Or is there some point where the straight serrations changed to scalloped on both lengths?
The 5" 5906 PPCs that I have seen all have straight slide serrations.

The 6" 5906 PPCs that I have seen all have scalloped slide serrations.

Now all the 5" guns had serial numbers lower that the lowest 6" guns that I have seen.
So here is the question . . . . Have these always been different on the two slide lengths? Or is there some point where the straight serrations changed to scalloped on both lengths?