This is a very early and collectible Ruger S22L commonly known as a 1AB in .308 Winchester. Serial Number 5xx it was made sometime between 1967-69. This is in the style of a light mountain rifle with no sights and a semi beavertail forarm, with wrap around checkering.
This rifle carries at least 12 points in Claytons book of No. 1 rifles placing it in the "very rare" category (0-4 nice rifle, 4-7 collectible, 8-10 Rare, 11+ Very Rare).
It has normal handling marks for a ~40 year old rifle and shows no abuse. Nice bright bore.
Will not ship to California.