Fab, there are 4 types of air rifles. Break barrel spring, break barrel spring/air assist, CO2 pneumatic's and PCP pneumatic's. Break barrel being the cheapest, PCP's the most expensive, bolt operated can easily go over $4,000. PCP's have to be pumped to over 3,000 psi, either by hand or using a scuba diving pre-filled tank. CO2 guns are too weak for hunting, ok for indoor practice, but very unreliable. Even though the product says over 1,600 fps for 177 guns, that's all hype. Actual chrono results are far less. And the fast pellets are also the lightest and least accurate. Generally speaking heavier pellets are most accurate. You may have to try several pellet weights to get the one super accurate your gun likes. The ideal velocity is around 800 fps. For squirrel depredation hunting, I used a RWS Diana Model 34 .177 cal single shot break barrel, with a 4x Center Point spring gun scope, 10.2 grain pellets for decades. Finally upgraded to a Game Swarm Fox 10 shot break barrel spring air assist in .22cal with a Gamo 4x spring gun scope running 14.3 grain pellets. Spring guns has to use spring gun rated scopes. My buddy uses a AirArms PCP (pre-charged pneumatic) high end sled gun ($5,000 with scope) with an 8x Zeiss running 16 grain pellets. It can shoot sub 1 MOA at one hundred yards. PCP's can use standard rifle scopes or dots.
If you intend of shooting doves, go with a .22cal. The 22's are inherently more accurate than the .177, sorta like a .45acp is more accurate than a 9mm, because of ballistic co-efficient.
