Gauges suggestion

Hi, I need some help: using a 23 joules carbine, with a target (small boars) at 20 meters is more effective the .22 or the .25?

Logically the weight and the shape/material of the pellets is important so I need suggestions about this point too.

In my country I can buy Gamo airguns at a reasonable price and I like classic style so I'm thinking about a Maxima, do anyone have found the best pellets weight for this carbine and this kind of use?

Grazie mille 



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