From what I've seen about the 1977 proof gulden, it is a lot rarer than the circulating example. I speculate that this is simply a prooflike coin, but do you think this is a proof? Either way, I wonder what you would think about the grade. Maybe I should look at my coins more often!
Not proof. I lived in the Netherlands for 15 years when they still had the guilder. I feel many regular strike guilders look like the one you posted.