Just a few of the variations to help give an approximate date of manufacture.
1962- It was a 850 shot repeater and a little longer than the later models. It measured approximately 37 inches long.

1965-700 shot measured approx. 35 inches long.

1968- Pretapped holes for the model 303 scope was added. (Not sure how many years they had the scope holes.)

1973- Square notched rear sight was added. Before it was V-notched.

1979- Safety was added. Magnetic feed with loading door on side was added. Previous it loaded through the top and was gravity feed. ALso the Velocity was boasted up to 325fps. Before it was 290fps.

1983- Wooden forearm was added. Previous it was molded forearm.

The later models should be easy to determine year of manufacture. The lot number located on the side of the barrel will be the year and month.