Which Caliber?

Hi Elno. "Would .25 calibers by nature be more accurate than .22 calibers? If so, by a lot? A little? Somewhere in between?"

I don't believe .25 caliber is more inherently accurate to 100 yards, but might be more accurate in a practical sense virtue of .25 being easier to attain higher muzzle and downrange energies with heavy to ultra-heavy pellets (25+ grains) that buck winds better at long range. Somewhere between a little and a lot.

"What is the single most important factor in air rifle accuracy?" Aside from the nut on the trigger, probably a good barrel.

"the other most important factor for me is reliability, so any advice in this area would also be appreciated." I've found regulated guns less reliable than unregulated guns.

 "any advice on a tank would also be appreciated." 4500 PSI!!!

It's not which caliber is more accurate, all can be extremely accurate, but more of a question which is affected by the elements the least. For your uses I would suggest a moderately powerful .22 caliber. Something like a Kalibrgun cricket, Taipan mutant/veteran, or an fx wildcat if your looking for a bullpup. Kalibrgun cricket rifle, fx crown, or maybe an agt vulcan tactical if your more into something that feels like a rifle.

.22 over .25 because ammo is much cheaper and a much larger selection in .22 with very good longer range performance. .25 is more than capable at these distances, and its what I mainly own, but I hunt more than target and .25 just has better terminal performance for hunting. .22 will also get you more shots per fill which means more shooting less filling your tank. The reason I recommend something with higher power is it will allow you to push the larger weighted ammo available. Larger weight ammo typically means better bc for better long range performance especially in windy conditions. Also obviously it allows you to push slugs more easily if your want to get into those as well.

If your looking at long range competition almost all the competition shooters are using .25 and .30, but the performance over a good .22 for casual shooting is minimal in my opinion.

The single most important factor when it comes to accuracy has to be consistency. Whether it be in velocity, ammo, or you. When it comes to personal experience I have had a benjamin marauder, a few crickets, a taipan veteran, and a taipan mutant, all of which have been super reliable with only basic maintenance (and I'm not really good at getting that done). Almost all the higher end guns will give you very good reliability, especially if you leave them alone and only make recommended adjustments (not major modifications).

Long story short if I was mostly casually target shooting I would own more .22's than .25's instead of the other way around.

Welcome to the sickness and you will probably own both at sometime in the near future.

The 25 has a slight advantage in the wind. You have better chance with a 25 shooting 100 yards outdoors on paper if you're using anything EXCEPT a Daystate Redwolf HP in 22 or an Edgun R3M in 22.

Shooting out to 100 yards, you will be looking at the HP version of something, whether .22 or .25. As mentioned above, other things equal, the .25 would have an advantage at 100 yards. Most important factor, the barrel, always, nothing else comes close. Top level shooters spend a lot of time selecting barrels. A good trigger is a requirement.Given the importance of making fine tuning changes, I would not recommend an electronic gun. With the right barrel, the choice of rifles is vast. If I had to recommend one, RAW. 

A 30 caliber RAW HM1000x works...

I do agree .25 cal is a all around caliber both performance and power