I have a RWS model 48 that is a side cocker. I don't know how much energy it provides but I think it is approaching what they call a magnum. I have a .177 caliber but kind of wish I had gone with a .22. Especially on more powerful guns the pellet is heavier, so its slower, and you don't have to worry about it going super sonic as much which can cause the light pellet to tumble. Also, you can glue a bullet primer to a .22 caliber and make an exploding pellet
I actually haven't heard of a nitrogen piston but I assume it just uses compressed nitrogen so you would have to find a place to get bottles filled and wouldn't be able to shoot when empty. Just an FYI, springers use a piston as well. Springers can also be different to shoot since the spring is released and takes a fraction of a second for the pellet to start moving and travel down the barrel. The gun starts to recoil before the pellet leaves the barrel so you have to hold the rifle still longer than a firearm to be accurate. Also, a springer has recoil both backwards and forwards so you if you get a scope you need one made for a springer because it will trash a firearm scope that is only designed for backward recoil.
And there are springer guns that have been in use for a really long time and still going strong. If you don't store one cocked the spring should last as long as you. The piston also shouldn't wear much and the only thing you might have to replace is the seal and I would expect that to last 20 years or more if you occasionally lube it. I'm not saying a nitrogen powered is bad, just what little I know about the springers. If you have a constant power source you might be able to shoot semi auto instead of a single shot which could be fun. I will have to look them up and see what they are. I think if you get a quality springer it will be something you hand down to your kids if you take care of it. They can be a lot of fun in the back yard if you have the room. Good luck choosing.
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