Constantine - In post No. 21 you said you had the exact same 870 described in post No. 20, one having a 20" cylinder bore barrel. I assumed it was either an 870 with a deer barrel or one of the many home defense/"tactical" 870s. Your photo shows an 870 with a long hunting barrel (I'd guess 30"), a standard hunting magazine and a full buttstock. Your 590 has a pistol grip, no buttstock and an extended magazine. I thought you were comparing 12 gauge pump shotguns with similar characteristics - particularly the barrel length - hence my statement "I am missing something" in response to your statement "way too big . . . ." So, I checked the specs of comparable 870 and 590 shotguns on the manufacturers' websites and confirmed what I suspected - the specs are virtually identical in comparable home defense models.
I have an 870 HD with an extended (factory) magazine. My low cost and very easy method of shortening my buttstock was simply replacing it with the youth model (which fits me better). Having tried it only once, I will never again (I hope) shoot a 12 gauge with a pistol grip and no buttstock.