As we can see when looking at Squall's Revolver Gunblade, or Seifer's Hyperion, neither have exit holes for bullets and, thus, are shown to certainly have no indication of being used for projectile means:
(
Note: In the FMV screenshot, the indentation near the end of Squall's Revolver Gunblade is simply a curve and not a hole; further, it's not even on the front of the blade; assuming it were an exit hole, the blade couldn't be straight, thus making for an illogical and impractical design; however, as we can see in any of the images of the Gunblade, the cyclinder and firing chambers line-up with the blade, in which case the blade
must be straight.
Squall Link 1.
Squall Link 2.
Squall Link 3.
Squall Link 4.
Seifer Link 1.
Seifer Link 2.
Seifer Link 3.
Seifer Link 4.
Further, none of Squall's other Gunblades have openings or hollow areas on their blades with the exceptions of the Twin Lance and the Punishment Gunblades (note, however, that these hollow areas begin a short distance from the firing chambers of the two Gunblades; were it the case that they fired bullets, while possible that they could traverse the distance between the two blades and exit before the top blade could pass low enough to interfere with their trajectory, the fact that the barrel would be so very short would produce inaccuracies in the aiming and firing; further, if the weapon were swung somewhat to the left or right, due to the area between the upper and lower blades being hollow, the bullets would go entirely off-target if the target were in the path the blade was following in the arc motions in which the Gunblade users swing them, thus, again, making for an illogical and impractical design):
Shear Trigger.
Cutting Trigger.
Flame Saber.
Twin Lance.
Punishment.
Lionheart.
Further still, when watching the opening FMV of the game, we see Seifer pull the trigger of his Gunblade as he is bringing it down to slash Squall's face and a gunshot can be heard at that moment:
Were it the case that projectiles were fired by these weapons, Squall would have been killed.
Something else worthy of note is that if one loses during the game and receives the Game Over screen, it shows Squall's Gunblade broken in half. The blade is
solid. There's no barrel running through the blade:
Linkage.
Something else to consider is that when using Scan on Squall, the following information is given:
Uses a
sword called a gunblade. Special skill is Renzokuken, using the gunblade. Silent, and a bit cold.
(Bolded for emphasis.)
The game itself refers to the weapon as a sword.
Something else to consider is that Seifer's Hyperion is more thin than Squall's Revolver, and likely lighter, allowing him to hold the weapon straight out with one arm, as he often does:
Linkage 1.
Linkage 2.
Linkage 3.
Linkage 4.
Being that this weapon can be held out straight with one arm, Seifer would easily be capable of aiming and firing with the weapon were it capable of emitting projectiles, yet he never does so. Further, being that Squall's weapons are all larger, bulkier, and likely a good deal heavier, they would be more difficult to aim and fire with. If one of these weapons were designed in a manner that would allow it to be easily used for projectile purposes -- as Seifer's would be -- then it would be illogical for the others to not be so. If these weapons had the capacity to emit projectiles, then all of them would be designed in such a manner as to allow one to use them to such effect. To design weapons that can fire projectiles, but not design them in such a manner as to allow one to easily employ use of them in that regard -- and design only one out of eight of them in a manner in which it could -- would not only be impractical, but extremely illogical. It would be akin to giving someone some Game Boy games, but no system to play them on.
Something else to note is that Irvine was sent with Squall's party to assassinate Edea because he was a sniper. If Squall's weapon had projectile capabilities, it's safe to assume that he would have been trained in the use of guns and Irvine wouldn't have been needed. While still arguable that Squall wouldn't have been necessarily trained as a sharpshooter, in light of all the other information against the possibility of the Gunblades having a projectile capacity, Irvine's presence being required certainly doesn't support the notion in any way.
Being that the weapons are never once used for projeticle means, have no exit points for bullets to leave a barrel from, are actually called swords within the game itself, are only used like swords, and with no one ever indicating that the weapons could be used for any means other than as a sword, clearly, they are simply swords with no projectile capacity whatsoever.