Among many others, I have the Hammerli 850 CO2 airgun in both 22 and 177.
For under $300 you get a bolt action 8 shot airgun that can take pigons or squirrles out to 40yrd. (Refub from the distributor for $140!)
Kit comes with a decent scope also.
My .22 has many thousands of rounds threw it. I shot it so much I bought the 177 because pellets are so much cheaper. Shot it also many thousands of times. Maybe paid for new gun with the savings. (maybe)
You can do a cheap and easy modification (called the spring mod) and increase the stock power 25%. Some guys have really tricked them out (20FPE in a CO2 is rare, but doable), I only did the spring mod. Dead pigeon is a dead pigeon, mod just made a 50y shot easier.
CO2 can be be a problem in very cold (50 or lower) or hot (90 or above) but in the 10 years I have been shooting CO2 guns I can only think of once when the heat was an issue. I left the gun outside in the sun and it got hot to the touch. It had valve lock (CO2 expands to much and locks the valve above certain temps, preventing firing). I put the gun in the shade and 10 minutes later in was fine. Not to bad for 8 different CO2 guns in 10 years and too many thousands of pellets to count.
I bought an R7 last year (medium power, small break barrel) that will shoot groups under dime size at 25y. For a break barrel, that is great. Best I have ever consistently shot in a non-match spring gun. Power is low, but the gun is a pleasure to shoot. And I can put a pellet in a birds head all day at 25y, no CO2, no pumping, no fuss.
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