Believe it or not, many questions can be answered just by reading the shooters handbook on occasion. Regarding the "copper washed" question, page 27 of the shooters handbook states,
REVOLVER AND RIFLE AMMUNITION
- May not be jacketed, semi-jacketed, hollow point, plated, or gas checked. It must be all lead. Moly-Disulfide, polymer coated bullets, or equivalents are acceptable.
When a bullet is copper washed or plated, it is no longer "all lead" and is therefore not allowed.
As for my go-to ammo for buckaroos, my 9 year old grandson shoots 38's and 12 gauge with no problems. He is 4'6" and weighs 65lbs.