This is interesting - my Janome 6600 is very picky about bobbins. I can't use the ones that came with my Brother CS6000i, nor the older ones that came with my 90's Kenmore, even though to me they look nearly identical. (Although the Brother & the Kenmore can share...)
It will work OK for a bit but then I get jams in the bobbin area. So I bit the bullet and bought the Janome brand bobbins from Amazon and no more bobbin jams. Hopefully you'll be lucky and your 7700 is less picky!
I should note - the bobbins I bought from Amazon were packaged in Janome packaging but did NOT have the "J" on them like the ones that came with my machine and are a slightly different shade of plastic. They work great, though.