When Ruger finished out the 220- prefix that was originally started with the 22/45, there were about 24,000 numbers left to fill out the 218- prefix (the Competition Target sold well, but with only one model couldn't possibly fill out a 100,000 gun prefix series), so Ruger went backwards on the 22/45 and helped finish out the 218- prefix with any and all models including the 22/45. When completed, Ruger jumped to the 221- prefix to "standardize" there serial numbering among all models.
Here's the paragraph that appears in the reference:
P4, P512, KP512 and P678GC with "out-of-sequence" 218- serial number prefix. Note that this was not a factory error, but was done so that all models could be joined within the 221- prefix. Known s/n range 218-73900 to 218-98627. Approximate quantities produced: P4 = 1,400; P512 = 7,000; P678GC (special Davidson's issue) = see above; KP4 = 285.
What is ironic is Ruger started all four Mark III pistol series' with different prefixes and they are again soon going to all be in a single prefix all but one series has already filled out its prefix.
Chet15
