It is a 1997, not a 1977- that would be a solid copper alloy coin.
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If I am not mistaken 2.5% of the coin would be copper. If that copper was removed the weight should be around 2.44g.
The plating only makes up a small part of that percentage, the majority of the copper content is actually alloyed with the zinc core.
The reverse picture is too small to see much fine detail but I see luster on the obverse so that would rule out post-mint stripped plating. Unfortunately, this is a very difficult error to definitively authenticate by photos alone but based on what I can see, it appears to be missing the copper plating and is a genuine error.