You need a police issued firearms license.
Only certain classes of firearm can be licensed.
For instance, fully automatic firearms are banned.
They can be used for just about anything except shooting humans… Targets, pests, venison back steaks, etc…
Canada is similar, you have to undergo 1st a firearms safety course and optional additional 2nd course for "restricted" firearms. You need also a 3rd hunting course if you want to use them for hunting. Most approved trainers will offer all 3 courses: 1st course is long-guns (e.g. hunting rifles), 2nd course (optional) for restricted (hand guns, semi-autos, etc.) and the 3rd hunting course (optional if you just go to the range to shoot).
You can also buy air rifles (limited to under 500 fps shooting speed) of either 0.177 or 0.22 caliber quite easily, no license needed at all. I think you need to be over 18. When you buy pellets the stores will record your ID as well (they ask for my drivers license and write it in their log books). I have a "spring air" gun called the Ruger Air Hawk with scope. It's a great target shooter, aka "plinker", to practice basic posture, breathing and aiming skills. You can set up a shooting range in your basement if you have the space or at the cottage or any other private field without any concern (there are obvious safety considerations and you need to be smart and responsible even with this, or you or others may get hurt):
I can tell you that with some practice using the scope (I have crappy eye-sight and wear glasses) I am getting groupings of under 1" at 50 feet and that's not even close to the tightness that pros get. The pellets even at that distance are still powerful enough to go completely through various cans, and will pierce thinner wood slats. Definitely you don't want to be on the receiving end of the rifle. But it is a convenient, cheap and easy way to get into target practice and learning about firearms.
Now back to the capacitor-overload-powered "gun". The idea is that when the capacitor explodes, it's contents vaporize and the resulting gas wants to expand and therefore forces out the projectile/bullet. The expansion ratio can't be very great and while it will probably shoot something out of a barrel, it will contaminate the bore and probably damage it on repeated firings. It seems expensive as well considering that an air/spring-gun can accomplish many factors of power greater pressure with an air piston (and also larger expansion ratio) repeatedly with no issues and without contaminating the bore, and no need for electricity at all. Just add pellets (which are inexpensively obtained at about 1250 for around $25) and pump away! Even if you could manage to shoot, crack open your barrel, reload a pellet, close the break-action, aim and shoot again every 15 seconds.... You would be shooting for over 5 hours straight and probably your arm would fall off from exhaustion, for only $25.
With a capacitor gun, I can't imagine how difficult it would be to reload a projectile and the "capacitor" propellant efficiently and consistently, hook it up properly electrically, get the proper electric charge going and have it fire predictably. It would probably be a very complex process that takes time to set up, and when fired will be unpredictable rate and time and power, with pieces of the capacitor flying around inside the bore scratching and contaminating everything in sight. So for anyone wanting a reliable efficient cheap consistent and safe firearm, using a capacitor is going to fail on all levels compared with even the most simple cheap air-gun and pellets, and provide way less power.
Also keep in mind that while I can only get a 500 fps air-gun without a license, once I get a license (1st course) I can own regular long-guns that take actual ammunition (i.e. "bullets") and also air-guns that are much faster.... 1000 or 1250 fps.... compare that to a rifle with regular gunpower ammunition that will be upwards of 2500 fps. Also they are extremely reliable, hugely higher velocities are available and heavier projectiles which deliver way more energy to the target.
I would be much more interested in an electric "rail gun".... NOW THAT IS SCARY and FASCINATING at the same time. I don't think they are going to make something more portable and safe any time soon but here is an example:
Here's another example of an electric railgun but you can see how pathetically slow the projectile is travelling, it even bounces off the glass bulb although makes it shatter.
Even an air-gun pellet would have gone completely through and into the wall behind:
The actual electric rail gun used by the military is a huge beast with awesome firing capability.... Reaches MACH 7 speed and the projectiles are massive. MACH 7 is around 7800 feet per second... compare that to some of the fastest rifle muzzle velocities at around 3500-4500 fps, just a bit over half that speed. The military electric railgun will shoot a 3.2 kg (7 lb) projectile to MACH 7. The .204 Ruger can fire a 32-grain (2.1g) projectile at around 4225 fps. So do the math... E = 1/2 mv^2...
3200g @7800 fps vs 2.1g @4225 fps. Not taking units into account or figuring out the exact energy, I just want to know purely the ratio... we have 1/2 x 3200 x 7800^2 compared to 1/2 x 2.1 x 4225 ^2, or 97344000000 : 18743156 is about 5193 : 1 difference in power at the end of that projectile between the military railgun and one of the fastest rifles.