Carolus II - 4 Reales 1683 - Segovia (Fake Or Not ?)

MathieuMa I think from the weight - you clearly suspect the correct answer. The coin is a forgery.

The surfaces of the coin are too porous and none of the design elements are sharp enough to be a struck coin. This is in all probability a casting.

Also look at the fields around the letters ARVM - notice all of the "soft" die breaks? These tiny raised lumps are seen on most transfer forgeries but are quite rare on originals and NEVER appear this often in my experience.

There is also a VERY CURIOUS split in the coin. Look at that closely and, I will bet, you will see proof positive of the forgery. Start at the M in HISPANIARVM - there is a split in the planchet that transitions into a die break just before it crosses into the lower right quadrant. How did a split in the planchet become a die break? The split crosses into the lower right quadrant of the shield without appearing as a break in some parts of the perimeter.
Then it concludes as a odd looking "break" in the field. The appearance of this "SPLIT" is NOT possible. The planchet split looks like a DIE feature to me that was either copied from the original coin or which was added for "believability". Check in the deep part of the split to see if the crack actually passes through the coin. I doubt it will - the base of the crack will be solid metal.

The only saving grace for a counterfeit of this period, would be if this is a contemporary circulating forgery. The Contemporary forgeries of this coin are worth $50 or more. However, based on the method of manufacture, I would theorize that it is modern and essentially has a value of under $20.

MathieuMa Weight makes a contemporary copy unlikely but not impossible.

It is however a nice looking fake that is worth something (about $20 would be my personal limit) - let us know if it gets refunded.