I put this question to the most knowledgeable person I know concerning the 1903 Springfield, John Beard, this is his answer.
“The "highest" confirmed Springfield Armory M1903 serial number is S/N
1592563. The serial number appears on a receiver fitted to a Mann Accuracy
Barrel once in use at the Frankford Arsenal proof house. The receiver was
pictured in the February, 1971, issue of "The American Rifleman." The
serial number, however, is a mis-strike.
The "last" known Springfield Armory M1903 serial number that was struck is
S/N 1536285. The serial number was reported on a USMC sniper rifle and was
noted by the person reporting as being unusually high. S/N 1536281 has also
been reliably reported and I have S/N 1536275 in my collection.
Fourteen serial numbers have been reported between S/N 1536285 and S/N
1592563. I have no doubt that some of the reports are legitimate. But, the
serial numbers are very widely scattered and are unquestionably mis-strikes.
As a matter of note, I have 107 serial numbers in my data base between S/N
1532878 (last "official" serial number) and S/N 1536285 (inclusive). The
average spread between serial numbers is 32. I have 15 serial numbers in my
data base between S/N 1536285 and S/N 1592563 (inclusive). The average
spread between serial numbers is 3,752. So, it's unquestionably clear from
my data base where the "last" legitimate serial number is.”
