The smallest caliber I really mess around with anymore is .25. The 14 16 18 gr .22 blow all over with the slightest breeze. Heck 25 grain .25 caliber is bad enough. With a .22 you have a smaller transfer port so you need a more powerful gun to push .22 heavier lead. I just find between 25.39 grain and 33.95 grain pellets most of my needs are met and still at a very reasonable price.
Trucker3573 makes some great points, I’m going to expand a bit as the original poster seems a newbie…
I own at least 12 high end PCPs - from most every “major” manufacturer, with barrels in all common calibers: .177, .22, .25 and .30.
There are certain “noteworthy” pellets that shoot great in a wide range of rifles and across a wide range of speeds:
.177 - JSB 10.3g
.22 - JSB 18.13g (15.89g also very good)
.25 - JSB 25.4g (34g also very good)
.30 - JSB 44g
Points to consider:
If target shooting mostly 40 yards and in, .177 is great fun and economical on both air and pellet cost.
If target shooting mostly 60 yards and in, .22 is a great choice.
If target shooting with a focus between 50 and 80 yards, then the .25 with 25.4g pellet is a great choice.
If you are thinking of target shooting a pellet gun mostly past 80 yards, then invest in wind flags now, lol - even with .30 caliber, shooting pellets past 80 yards is a wind reading challenge.
Truckers point about heavy .22 pellets is something I don’t think newbies understand…
Because the back of a .25 25.4g pellet is fatter, it provides more area for the air to push against vs a .22 25.39g pellet.
This results is the .25 caliber shooting 25g pellets being able to use a lighter “tune” (lower regulator pressure and lighter hammer strike) to achieve similar velocity than a .22 caliber shooting 25g pellets.
I’ve found using a lighter tune enables accuracy and provides an overall more enjoyable shooting experience.
Finally, you will find the cost of shooting 25g pellets about the same with .25 and .22 calibers (350 pellets to a tin).
The gap between .22 and .25 is not that much - compared to say .25 vs. .30. So it’s really more about the distance you see yourself shooting most often.
Just some things to think about. Every newbie starts out thinking “yeah, I’m gonna be shooting targets at 100”… Then you do it the first time…
… 100 yards is a lot of walking, lol. You will need a high magnification scope to see your pellet holes at 100. You will need a calm wind day the first time you try it… or a really big piece of cardboard to make sure that you’re “on paper”…
Be realistic about your distance, then pick an appropriate caliber to start. They are ALL fun!
-Ed