Hi,
The 521T (TL) was introduced in 1947 and discontinued in 1968. About 66,000 were made. It used the same action as the 511 and was a junior or intermediate target rifle. It had the same stock as the 513T.
The government bought about 1800 of them for marksmanship training program. That was the first one I shot. It was beat up, but shot better than I did. I think they are great little rifles, but then again I'm a little biased.
George