572 Fieldmaster date code

[dmccarley1979]

I have a 572 fieldmaster 22 that my grandfather left me that i've had for years. i remember him having it and using it regularly in the early 80's. I have tried to search this out, but I'm confused. Stamped on the side of my 572 is a diamond shape then "XY" then just below it and slightly to the right "78". according to the remington date codes, xy would be december 1930, which is not correct since they didnt start making the 572 fieldmaster until 1955. i does have a serial number stamped into the receiver so i know its after 1967 and would assume its 1978 except someone posted that a code of showing 78 was made in 77.... i think confused is an understatement. Anyone have any information that will tell me when this rifle was made.