I have PCPs in .177, .22, .25, .300, ,308, .357, and .45. .25 is by far the most versatile.
Now in Florida, to deer hunt with an airgun the caliber had to be .30 or above. So I often carry my .300 or .308 afield as it allows me to legal harvest anything I may come across in the proper season. But a .25 of proper power could take anything I’d want to. I’d even take a Florida sized whitetail on a lung shot with the .25 if using a heavier bullet and a soft-lead HP if it was otherwise legal.
I do have a .30 carbine that is an amazingly versatile gun, but its a custom build. That model comes in .25 by default.
Here’s the .30 carbine with a light thermal on a coon hunt.
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