How did you decide what caliber to get first?

Hello only you know what is best for you. Make a list of pros and con for each caliber, how far you shoot, what you are shooting(size of pests), cost of ammo, availability of ammo, caliber available in gun you want, etc. Hope this helps and good luck with your new new gun Eric.

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This. And then there's the slug thing lol. With slugs, .177 is now approaching the FPE levels or equivalent to .22 shooting pellets, .22=.25, and .25=.30 depending on the platform and appropriate speeds. Also consider that the bigger the caliber, the lower the shot count if mainly plinking. 
 
Hello only you know what is best for you. Make a list of pros and con for each caliber, how far you shoot, what you are shooting(size of pests), cost of ammo, availability of ammo, caliber available in gun you want, etc. Hope this helps and good luck with your new new gun Eric.

Eric offers good advice above for you. In case you haven’t made a lot of research on different calibers, .25 is quite a bit more expensive, harder to find and has less choices than .177 and .22. If you go with .30, it’s going to complicate things even more than a .25 with all the disadvantages I listed being even worse. The bigger calibers do have the advantage when hunting larger game/pests and it really depends on how you plan to use it that matters. 


 
Power, cost, availability, variety, and air consumption.

I shoot a lot of .22s and I will say this.... the difference in flight time between .177 and .22 as well as drop. Both in 900+ fps guns, is HUGE out at 50+ yards. Now, larger calibers do have less drift in wind, but it's not really windy where I shoot.

Comparing 21gr .22 slugs at 950 fps to .177 JSB monster RD at 900fps 
 
I know for me .22 pellets are easier to find. Well not at Wal-Mart but after I got the impact that can do a barrel change, I thought sure lets try a .25 Thats when I found out, boy not as many pellets per tin, harder to find, especially the ones that the impact likes. And boy the .25 blows a big hole in the rats does not stop and just keep going. The .25 for me was louder too. Maybe too loud for the backyard.
 
You've state that you want a .22 next, so go with your initial choice. The .22 is a very versatile caliber, different than your .177, but alike in that it is popular and typically widely available. The determining factor should be the size of the animals you're going after. Largest critter I would take is a woodchuck so for me a 30 ft. lbs .22 is plenty powerful. Plinking with a .25 or .30? Pricey and mucho air consumption.


 
If you're in it for the long haul, eventually you'll end up with all 4 main calibers and purpose-driven airguns for each scenario lol. I can't be the only one who first started out with .177, .22, .25, and .30cal and in that order.





This exaclty.



I started with a 22.. worked my way up to a 25.. then down to a 177.

I really enjoy my 177.. cheap to just hit paper. 

177 is cheapest to plink, as there ismore of a selection.. 25 is much harder to find pellets and feed.

22 is a nice all around and a ton of selection. 
 
 Before I went down the rabbit hole like a lot of people on this form did I Already had one one177 caliber that What is a multi pumper and then I bought a springer Then a Crossman custom shop 2300 And kept them all the same that way I could shoot the same pellets and all of them and would be cheaper. I quit hunting a long time ago and just plink and target shoot.So it is really going to depend on what we are going to do with your airgun.
 
I will add my two cents: I started with .22 matador r3, then got a kalibrgun carbine .25, a raw .22, then got a .30 r5… and lots of others in between that dont get shot much.

Now I have just ordered a steyr hunting5 scout .22 and a kalibrgun carbine .22. 

My choice is for .22 because

- I prefer lightweight carbines over bullpups, I love to shoot standing unsupported, and i find carbines more ergonomic (for me)

- with .22 you can still have somewhat shorter barrel and get decent combination of efficiency, speed/power and noise. 

- anything .25 or larger required long barrel or you get bad efficiency / low # shots. And there there is no such thing as a short lightweight quiet .25 or .30

Bear in mind: i have a 50 yard range in my garden, i dont hunt, and am not in a gun-friendly environment. My .30 is for windy days, the scout is for fun, and the kalibrgun is just for tinkering with… 
 
.22 Is very, very good for small birds up to 120 yards (without wind).

In my personal opinion is a small caliber for jackrabbit and bigger, (not withstanding I have taken a Jabalina with an Evanix Ar6 .22 cal. And my nephew a bobcat with that same rifle. But the power of AR6 is above 60 foot pounds).

For almost everything I use the .25 (allows me better accuracy in real world at above 90 yards)

When real hunting, I use the .30 

When deer hunting I use the .357

If you try to keep a good storage of pellets and always have a minimum of tins before the next internet order of pellets, you won't suffer when there are not available at Pyramydair or AoA or form whomever you buy them.
 
I'm not sure if this advice will be helpful because a lot of people do not want to deal with casting their own projectiles.

I looked at this is something that was the start of a long term hobby and I wanted to minimize my repetitive spending. Best thing I did was get a mold and a gun that could shoot the bullets well. 

my point? This is how I ended up selecting 25 caliber as opposed to .177 or .22. There's no easy way to cast your own .177 as far as I can tell, and the .22 molds that were available from the suppliers I knew about were not as interesting as the 25 caliber molds.



Now i have a range: 257, 25, 22, and 177 I always find the 25 or 257 most fun to shoot