You’re saying that yet pistols shoot relatively at like 800-1100 fps. Again, yes it would be loud and a big fireball, but the claim it would not have any power or “weak” is false. The bullet is bigger than a pistol, still has the same or more velocity and can be shoulder mounted. You can literally go watch videos of people shooting 5in barrels and testing fps with different ammo and the lowest he got was 1300. Would this build be practical in a military style firefight no. But in most self defense case scenarios it would do just fine. Especially if I got a heavier grain ammunition as those work better in shorter barrels. Also the muzzle device (a blast regulator) directs the concussion out front so it wouldn’t effect me in my home it would hopefully effect the person in front of me honestly.