The science behind Squall's Gunblade, if there is any?
After reading the information on Gunblade wiki, Squall's - and Seifer's - Gunblades do contain a barrel that runs through the sword. When the trigger is pulled, it emits a shockwave that deals additional damage when it strikes the enemy. 


  In Final Fantasy VIII gunblades have a sword blade with a gun action built into the hilt, the barrel running inside the length of the blade. They are mostly used like normal swords, but triggering a round sends a shockwave through the blade as the weapon passes through an opponent to boost damage


The reason behind this design was that Tetsuya Nomura was looking for something to further engage the players.


  The gunblade was designed by Tetsuya Nomura for Squall's weapon in Final Fantasy VIII with the aim to make the battles more dynamic, the players needing to press a button at the correct time to deal a critical hit, and to give Squall an iconic weapon.


Seeing how this was the first game in game franchise to use the style of weapon, it is no surprise there were some design flaws in the implementation. 

Furthermore, later games in the franchise still use Gunblades and they expanded on this style of weapon to allow both shooting and slicing