most fill to 3000 PSI. Don't buy a SCUBA tank as most are only 3000-3200 PSI. There are many carbon fiber bottles that hold 4500 PSI. Depending on the volume of the tank, you can fill your gun multiple times. If there is a SCUBA shop in your area, they will often be willing to fill your tank. Some fire departments will too, ofr a small donation. As mentioned, some paintball shops will fill tanks too. People with bad backs will NOT want a pump. Those that do pump usually only fire a few shots, then top of the tank. Much easier that way. If you use the pump a lot, you will occasionally need a rebuild kit due to heat from friction. Airgun scopes are usually rated for the dual recoil of a spring piston or gas ram airgun. Don't forget they are parallax adjustable down to 5 - 10 meters. This is very handy for airguns and rimfires. PCP, CO2, and pump-up airguns have no recoil to damage scopes. Compressors vary a LOT. Some fill faster than others. Most need regular maintenance. I prefer .25 caliber for hunting, but .22 is more popular. Most .177 cal. airguns get tons of shots between refills. Many PCPs have shrouded or suppressed barrels. ATF is OK as long as they cannot be easily removed and put on a firearm. Have a TON of fun.