The difference in a rifle where you only change the caliber is what in Internal Ballistics is called Expansion Ratio. It works in firearms and also in pellet guns.
The most intuitive way of explaining expansion ratio is by making you think of the following:
The piston is in front of the same spring, right?
It has the same weight, same area, same impulse.
Therefore, it is expected that the powerplant will develop the same pressure curve/spike, right?
OK, now, think in terms of pressure: Force divided by an area.
If the pressure is applied in a small area (0.177" cal. pellet) it will produce some force; BUT if it is appplied over a LARGER area, like a .22" pellet, it will produce MORE force.
So, we say that the expansion ratio of bigger calibers is better for the same pressure curve. Ergo, there is MORE energy TRANSFER from the powerplant to the projectile.
If a powerplant cannot transfer all its energy to the projectile, it has to go somewhere. In firearms it goes up in flash and smoke, literally. In Spring guns it goes BACK into the mechanism, either as piston slam, or as spring overcycling.
THIS is what damages the gun. Either too heavy or too light, is not good.
Airgunning, as most things in life is the "art of a happy medium".
Every now and then we DO find exceptional barrels that shoot well the heavy for caliber pellets there are out there in the market. In that instance, by all means, if they shoot well, use them.
But do bear in mind that the gun itself tells you where she is happy.
She will transfer the highest amount of energy to the pellet where she reaches her OWN happy medium.
That is why we all need some access to a Chrono, to see where our guns are happy. I'm not saying that we should all buy one, I am just saying that the best way to determine which pellet weight is most useful to YOUR gun is by using one.