The QB79 Repeater uses a different bolt to that of the standard QB79. The Repeater bolt is based on the XP Tune bolt and that - together with the superior breech seal compared to the single shot factory gun - is the cause of the higher muzzle velocity in the Repeater. There's over 20 different parts in the Repeater when compared to the factory, single shot QB79...
Answering your question about 700 fps muzzle velocity in a standard gun is somewhat complex. The muzzle velocity of any gun will vary with the pellet weight. And, with any CO2 gun, the temperature makes a big difference also. For example, the muzzle velocity of QB78-type guns varies by about 2 fps per degree Farenheit. So a gun shooting a specific pellet at 600 fps at 65 degrees F will shoot the same pellet at about 640 fps at 85 degrees F.
The muzzle velocity numbers we quote are with "real world" medium weight pellets - 7.9 Grains in .177 caliber.
I'd say that it might be possible for a .177 factory gun to - just - reach 700 fps with the lightest possible (eg 4 Grain) alloy pellets shot at 90 degrees F +. But with an unmodified gun shooting medium weight pellets in average temperatures, no.
I hope this helps,
Archer Airguns Inc.