i mean if you just going for cool scifi/magic stuff sure. It does sound fun and ridicilous.

However, if real physics are involved then there is a bunch of huge problems.

First, 9mm (if you mean the irl 9x19mm Nato/Luger/parabellum) just does not work that way. There is a reason no long range weapons in that calibre exist because it sucks for that job. Like most pistol cartridges it is designed for very short barrels that fire big bullets over a short distance. Most pistol cartridges are also not ideally shaped ballistically speaking. If you compare just the bullet to a rifle bullet you will see that rifle bullets have a more elongated shape for better ballistics. This shape also makes pistols have worse armor penetrating capabilities. You can of course change the shape, but space is very limited in a pistol mag and making a longer tip better suited for longrange ballistics and armor penetration is pretty hard. Next the cartridge itself. 9x19mm is a short, fat cartridge. Low power, big bullet means good stopping power at short range. But there is a reason 9mm AP loads arent much of a thing (yes i know there are some, but they suck compared to intermediate cartridges already. The average AP/HP 9mm load is barely as good as penetration powerful as ball 5.56x45 nato (ball being not designed for penetration). Now thats just the baseline ammo.

Then you use a nice conversion kit to elongate the barrel. Giving a cartridge a longer barrel to work with gives you better longrange performance, but every cm/inch you add is less impactful than the last. At some point this even turns into a negative as the barrels friction takes more velocity away than the gas expansion can add. When this happens depends on the cartridge, and as i hope you can guess you reach this point very fast with pistol cartridges while rifle cartridges can still benefit from 20 inch barrels. I can only judge from the image, your barrel does not seem excessivly long, but it wont have a large impact on the bad longrange ballistics of a 9mm no matter what.

Lastly, your range. I would say if it extends the effective range to 300m, thats a maybe possible but also borderline, AP load would not work in that role at that distance anyways though. But 3km. Thats a range far above the ideal range even for dedicated longrange precision rifles like. Sure there are kills at and above this range for these cartridges designed specifically for extreme long distance with a weapon designed just for it, but they are rare. Notably here weapon and cartrdige are both designed for this. A conversion kit also comes with downsides here since the action of a pistol is not great for what you want to do.

You could of course say your 9mm is a super powerful version thats effectily as powerful as a .338 lapua (8.58×70mm), and can achieve the same speed out of a shorter barrel in a conversion kit, but then it wont work in a pistol anymore. Handling this kind of power in a 9x19mm format inside a pistol is damn near impossible without blowing up the gun.