This is just an opinion of the airguns that I have owned. I can only assume you mean both guns and rifles, not just guns (Like you said in the question). Most collectors and longtime users consider the Sheridan "C" Series air rifles and the Benjamin 392 or 397 the standard that all pump air guns are measured by. They are so well made that they last generations and have a considerable amount of power.
The Sheridan C9 is a .20 caliber
The Benjamin 397 is a .177 caliber
The Benjamin 392 is a .22 caliber.
You can not go wrong with any of these models.
It depends on what aspect of the environment you are looking to improve. In any environment, it is the native species which are the best.
The best way of reducing emission of carbon dioxide is to use carbon-free or reduced-carbon materials
oxygen and carbon dioxide
Carbon dioxide is best described as a compound, specifically a chemical compound, because it is composed of more than one type of atom chemically bonded together (in this case, carbon and oxygen).
The dome pellet is considered to be the universal pellet.
Air is best.
it is a product
The best way would probably be to chemically decompose the carbon dioxide into carbon and oxygen.
used in protiens
Air contains all of these gasses as a mixture. Carbon dioxide is a chemical compound (molecule) Carbon (C) and Oxygen (O2)
The best for what? Paintball, .177 Pellet, 6 mm pellet or bb rifle?
Some of the best pellet stoves are breckwell.com and lennonxhearthproducts.com. You can also check out englanderstoves.com.