Gunblade models don't need to be so extra...

[TouchandFeel]

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The idea of a gunblade's cartridge exploding and creating vibrations in the blade that increase it's cutting power is based off the idea of the vibroblade, a type of weapon commonly found in science fiction, although real world adaptions of the concept have been developed for use in scientific and medical applications.

A vibroblade is basically a bladed weapon, usually being a knife or sword, on which the blade is vibrated at an extremely high frequency.
The science behind how it works is that the high frequency vibrations of the blade cause the blade to move back and forth in incredibly fast but microscopic movements, creating a concentrated sawing motion with the blade. Since the edges of blades are more effective at cutting when drawn across what is being cut as opposed simply being pushed against it, the vibrating of the blade and the accompanying sawing motion that it creates increases the cutting force of the blade.

Now realistically, the explosion from a bullet cartridge is nowhere near enough to cause vibrations in a large metal blade in the way a vibroblade works since the vibrational frequency would be much lower and the energy would dissipate into whatever was being cut very quickly since the vibrational force occurs in only a short burst instead of being sustained. However, while the vibrations in the blade would be much lower in frequency and energy compared to a vibroblade, the additional movement of the blade from the vibrations during cutting would likely result in the cut not being as precise and clean, leaving a not as deep but more ragged wound which could end up being more deadly.

As for recoil on a gunblade similar to a regular gun, there probably would not be any or if there was it would likely be greatly diminished.
Recoil when shooting a gun is basically Newton's Third Law of Motion (for every action there is an equal and opposite reaction) playing out.
When a bullet is fired from a gun, the force of the bullet cartridge explosion propels the two parts of the bullet cartridge, the casing and the bullet itself, apart in opposite directions. The bullet is expelled from the gun at high velocity, while the force applied to the casing which is still within the gun is transferred to the gun itself and this is what recoil is.
In the case of a gunblade, the force of the bullet is transferred back into the gunblade as it strikes the blade to cause the vibrations and so you end up with opposite forces pushing on the gunblade in opposite directions which would likely nullify each other out. There could potentially be a slight jerk in the gunblade as the cartridge would likely start to exert the backwards force on the gunblade immediately while there would be an almost imperceptible delay before the bullet strikes the blade and exerts a forward force on it, counteracting the backwards force already applied.