Yep I agree, I miced mine the other day (found it in theback of my gunsafe) and it was .695. But it is NOTHING like the .695 Rhino I hunt with. As for getting under .680 with a 835, be careful. The 835/935 are built with 10ga backbores (Redneck Bill that is why your slugs stuck, you must not have read the "NOT FOR USE WITH SLUGS" warning on the barrel of your 835?) and are THE finest turkey guns on the market if loaded to maximize the payload ability.
I have a Supermag 870 as well and was shooting Nitro in it until I toured Nitro Ray's "shop" a couple years ago in MO. He found out I had an old 835 sittin in the closet and convinced me to dig it out, shoot the Nitro/Rhino combination and needless to say my 870 is now a backup only gun! Sure the 835/935 won't show you what it is made of if you stick simple 3.5" loads in it just like you would anyother 3.5" gun. But if you try some ammo specifically built for it, you will see an incredible machine once you pass the 60yd mark!!!
Good luck and don't under-estimate that cheap ol Mossberg trombone,
RA