Welcome to the Forum!
As noted,, a "Chief AJ" gun. Do a little research into guns he built, and you will find a ton of info.
As for the serial number look-up. Were you looking at the Ruger web site?
There,, they list the first number for that year,, and then the first number for the next year. It often confuses people thinking that Ruger skipped something.
Our best reference is the Red Eagle News Exchange Guide.
It shows a serial number range.
In 1998,, they went from 247-34572 to 249-06698. So your gun was a 1998 made gun.