Not trying to stifle your creativity, but the first question you should ask is "What problem does this solve?" and "What can this do better than what currently exists?". If it doesn't really do either, you're not going to have much of a market for it. My issues with it.
#1. Not sure what problem it solves or that it does something better than what currently exists. Is it more reliable, more concealable, easier to operate, more accurate, lighter, etc...
#2. You drew up the gun as a .22 LR which is a horrible defensive cartridge, especially if the other guy is carrying something bigger. You could conceivably use any rimmed cartridge, but your design requires that your "cylinder" be sufficiently robust to not blow up when fired.
#3. Going with a "straight" cylinder adds unnecessary weight compared to an autoloader. An autoloader breech is reinforced to handle the forces from the explosion of the gun powder so the mags can be very thin and light. You can also fit more rounds in the same space with a regular mag since the rounds can be stacked together and the breech contains the blast.
#4. Creating a "vertical cylinder" adds unnecessary bulk compared to a rotating cylinder. It makes it more unwieldy and possibly less reliable dues to the issues mentioned. Also as mentioned, it looks like it would need 2 hands to operate.
A few items you could do for your current design:
1. Make your mag extend to include the entire bullet like on a revolver. That way your mag/cylinder can be like the forcing cone on a revolver. You had better have a VERY RELIABLE AND PRECISE way to line the mag/cylinder with the barrel, or you're looking to blow up the gun.
2. Figure out a way to reinforce whatever holds the rounds in the back and protect the back of the rounds to prevent accidental discharge. Without a barrel, it won't have that much force, but the mag will still direct the bullet and hot gasses forward.
