I have an Air Arms S410 E in .22 cal., a PCP (pre-charged pneumatic) made in England. It is a bolt action receiver with a 10 shot rotary clip. The power source is a mounted tubular air reservoir, below the barrel of the rifle. The reservoir is pumped up with a hand air pump or from scuba tanks or a high psi compressor. The air gun can be pumped up to 200 bars or about 2,900 psi. The gun comes with what they call a suppressor which does quiet the discharge down considerably. A large variable power scope tops it and when shooting targets you don't aim for the rings or bulls-eye but at the little numbers printed on the rings, the gun is that accurate! Accuracy starts to fall off after about 5-6 clips are shot but shooting at approximately 1100 fps that is not too shabby.
Squirrel hunting with this gun is different. The sound of the impact of the pellet on the squirrel is louder than the guns report. The S410 E is a very effective small game gun. The down side is they are pricey and pumping the air tank up with a hand pump is a work out. The rotary clip will only handle a flat faced pellet so you are limited in pellet selection.
As mentioned before a spring type air gun will destroy a scope made for a rim fire rifle. If you do put an air gun scope on a Springer, you will need to put a scope stop at the rear of the mount. The recoil will vibrate the scope to the end of the grooves and the scope will simply fall off if you don't.
None of my air guns will replace my rim fire and center fire guns but likewise they will not replace my air guns. The air guns have their niche and are a heck of a lot of fun to shoot and you do not have to wear ear protection.
These are not BB guns. Lewis and Clark carried a .46 caliber, 20 shot, air rifle on their expedition and it was a powerful and accurate weapon. Their mission would probably have failed without it. You can get .17, .20mm, .22, 9mm, .45 or .50cal. in an air rifle. These larger calibers are used for deer hunting in Europe.
Attached is an air gun forum that will answer some of your questions. Keep in mind there are fanatics and air gun fanatics are as bad as tractor fanatics.
Airgun forum