Pre-Charged Pneumatic Rifles (PCP)
This is the group of rifles that has advanced the most in the last 10 years. They use a reservoir built into the gun to hold a store of compressed air, usually about 2500-3000PSI. This reservoir can hold anything from 30-500 shots worth of air depending on the size of the cylinder. The compressed air cylinder is charged via a hand pump or divers bottle. The regular spray compressor, garage pump or foot pump will NOT do the job as they do not run at high enough pressure.
Huge choice of brands and specifications - many multishots available
Great choice of add-ons such as silencers, bipods and custom parts
Accurate, high power
Very quiet with a silencer fitted
Cost of initial setup, Can be inconvenient to refill
Whilst no recoil is great for accuracy, it also takes away some of the fun and challenge of shooting.
CO2 Powered Rifles
This is a good way of buying a recoilless gun at a cheap price. They use small 12 gram CO2 cannisters or paintball bottels. CO2 powered rifles are mainly purchased as fun guns to use for informal target shooting in the backyard. No recoil and bolt action cocking makes them popular with beginners, younger shooters and shooters who struggle with the weight of a spring rifle. Unfortunately there are not many choices available.... but the available models are all great.
The main advantages are they are cheap to buy, recoilless and lightweight. They are whisper quiet with a silencer and make perfect short to medium range pest control rifles.
CO2 also has some disadvantages. You have to keep buying CO2 cannisters and they are limited in power.
Spring Piston Rifles (springers)
The gun is cocked either by breaking the barrel or underlever depending on the type of gun. The gun contains a piston and a large coiled spring. This procedure compresses the mainspring and moves the piston back, which connects into the trigger mechanism. When the trigger is pulled the mainspring is released, pushing the piston forward which pushes the air in front of the piston through a port and propels the pellet down the barrel. The movement of the spring and piston leads to recoil, which can affect the accuracy of the gun. With lighter rifles you usually get more recoil. For that reason heavier spring guns are often easier to shoot and more accurate. To shoot a recoiling rifle accurately, techniques must be learned to compensate for the recoil of the gun.
Initially cheaper than a PCP rifle, self contained
Generally single shot only, more noisy than a PCP to shoot due to muzzle and piston noise, recoil can make the gun more difficult to shoot accurately, requiring more practice.