Yep, sorry, but it's a replica. It's not just a "die match" for the one in the fake reports linked to above, but they are both clearly cast copies of the same piece, with the same flaws in the same places (both off-centred in the exact same way, both having the same V-shaped indentation at 9 o'clock on the obverse, etc).
If your grandfather was not a coin collector and/or doesn't remember how he got it, then it's likely to have been a Reader's Digest giveaway gimmick, or something like that.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis