check the date code stamped on the barrel. Remington Society of America, Manufactured Date link has the details.
Means it was made in February 1942. See related links.
Remington Arms introduced this model in 1939 and discontinued production in 1963 with an approximate number of 381,267, units built. The codes AG would place the manufactured date to March of 1960.
Google Remington scoremaster model 511. Several websites have information on this .22 firearm.
It's November 1941 or 1963 depending on if it's fairly low serial or a very high one, that date is either third year or last year production.
Try e-gunparts.com
xx is 1951 but there is no month code y (blackpowderx) are the valid letters for month.
Brownells Montezuma, Iowa
50-250 USD
grades are not marked, the date code is on the left side of the barrel near receiver (see link) those marks are inspector marks. I believe the only want you tell the grade of a 511 is the sights.
I bought a Remington 511-X (1964) this week at a pawn shop. I paid $175. There was a copy of a gun Blue Book on the counter, maybe not the latest edition, but it listed the 5411-X at about $175 for 80% finish, IIRC.
midwayusa.com product #698420 $20 + shipping phone # 1-800-243-3220