Well, you will have to clarify what you mean by perform.
I can't give you advice on slugs as I don't use them, but as already stated above, with the same weight and muzzle energy, the smaller caliber will have a better BC. For hunting though, I'd probably still get the .25. The difference will be there, but might not really matter for practical hunting distances. It will matter more if you're a champion caliber target shooter and you're trying to squeeze every bit of performance as you can... at which point, why not start looking at even heavier and maybe even larger calibers. You don't have to shoot the same weight .25 and .22. If those are the two calibers in question, you can always shoot a heavier .25 and then the question about differences in BC starts to even out.I am personally wrestling with this decision on a new purchase and would like some clarification about to what degree a couple points made in this thread. I am most concerned with accuracy with slugs for hunting small game between 75 yards to 125 yards with a crosswind. Does a .25 cal resist a crosswind better because it is heavier, or a .22 because it has a lower profile and higher speed. Also, as far as air usage can anyone give an estimate with a shot count shooting .22 and .25 with the same grain weight at the same fps? Also some mention the .25 is louder. What is the source of this loudness? Is it the sound of the impact or something to do with the projectile speeds entering the trans sonic zone between lets say 950 fps to speeds to 1100 fps at the muzzle? Inquiring minds want to know.
The reason why the .25 is more efficient is because there's more area for the air to push against. I read many times people always say that a .25 will use more air and be louder than a .22. in my experience though, that is not always the case. Assuming the guns are tuned properly, it really comes down to the guns' designs and setup.Thanks for the well thought detailed response it helps a lot as I had some wrong understandings. Why does the 25 use air more efficiently power for power? I find myself hunting taking shots hunting typically between 40 yards to 100 yards. I would probably take more shots at 100+ but since I only have 27fpe in .22 at the muzzle the drop off in energy at those distances starts to get questionably ethical. However, I am looking to step up to a new air rifle shooting 50 fpe at the muzzle so with a heavier pellet or slug I could carry good power at that longer distance. My intuitive sense says that shooting a heavy 22 slug would give me a better BC and accuracy at that distance. Just to make sure I am understanding you, are you saying the .25 is better for power and accuracy at that distance and more efficient using air translating to a higher shot count per fill as well as more power and accuracy at 90 -125 yards?