Double shot increases the burst rate of fire from 1/s to 14/s, so guess that's what the 1400% means.The way the numbers are presented is a bit confusing. The burst size and clip would make more sense if they were exactly 2 and 8, since that means 4 full volleys. It would be fun to have a burst size that was literally +2 (meaning 3), but then the clip size would be 11 and the last volley would always be short.
Ammo capacity +68% means about 303 rounds in the hopper which is also kind of a weird number. That's less than high capacity's usual 360.
+1400% burst rate of fire has to be as close to instantaneous as the game can do.
Double shot also increases the burst size from 1 to 2, and clip size from 3 to 6. High capacity also raises clip size from 3 to 6 so I guess you're right with the 2 and 8.