mod 51 means that numbers cycle between 0 and 50. For example, 51 mod 51 is 0 because the numbers have completely cycled and have returned to the starting point. 52 mod 51 would be 1, 53 mod 51 would be 2, and so forth.
The absolute value of 51 is 51.
Made 1960-1974. Value is based on condition, but roughly $275-$350.
The value is 51.
1964 mod 101 = 45
1970 - 1987
100 years (approx) sn pa20568
I think it should be 7.62 x 51 mm ...
@1970
999 MOD 1000 = 999
$100
It is possible
Since the mod 37 is a pump gun and the 51 is semi-auto, if it fits then it is a coincidence.