TL;DR: plasma weapons just aren't really very good. Yours seems unlikely to compare favourably against almost any other kind of weapon.
Here's the problem with guns that fire plasmoids like this: hot, pressurised gas expands.
In order for your plasma gun to be useful, the plasmoids it throws are gonna have to be quite warm... tens of thousands of kelvin, maybe. They're also going to have to be quite dense, because a blob of low density gas is going to have pitifully low momentum and so is going to be unable to bash its way through the dense atmosphere you might find at eg. sea level on an Earthlike planet.
A hot, dense blob of gas might also be called a "fireball" or even "explosion". In a vacuum it will expand at something like the Alfvén velocity or ion acoustic velocity, which are likely to be measured in hundreds of kilometres per second. This process will happen more slowly in an atmosphere, but not that much more slowly because your plasmoid needs to be dense in order to push through the air and so the relative density of the atmosphere will seem pretty low.
Clearly you need to project your plasmoid at velocities exceeding its expansion rate, and that's gonna mean at least 100 km/s, and that means you need a pretty fearsome accelerator in order to accomplish the task in a compact weapon.
How much power will this all need? Well, its very hard to say, but the only real world example of a plasmoid weapon that we have is MARAUDER, which used a power source called SHIVA STAR. This used a multi-megajoule capacitor (not too inconvenient) running a multi-hundred-kilovolt levels (that's more inconvenient) and capable of discharging in about a microsecond, yielding peak powers on the order of terawatts. That's going to be exceptionally difficult to miniaturise without creating something that will immediately blow itself to bits, likely killing the operator and/or vehicle it is mounted on.
MARAUDER threw its plasmoids at several thousand kilometres per second, and they hit with the force of a few kilograms of TNT. It won't have any substantial ability to penetrate armour, because the bang isn't very big and the density of the projectile will be far lower than conventional armour-penetrating rounds and shaped-charge jets. MARAUDER was intended for use against Soviet ICBMs which are a bit more delicate than even lightly armoured vehicles or buildings.
Lets compare that briefly with something like an antitank rocket launcher, such as the classic bazooka. These can throw a couple of kilos of warhead a few hundred metres fairly promptly. You can build it with 1940s technology, it can survive use and abuse by GIs, it has been proven to be cheap and effective even against heavily armoured targets. Modern descendants like the Javelin are guided and can wreck even the latest generations of heavy armoured vehicle.
It would make more sense to use guns, railguns, lasers, rocket launchers or electron beams instead of shooting plasmoids... basically anything else is likely to be better.