certain misdemeanors are fine but absolutely no felonies. if you get caught with a gun and you are a felon, thats bad bad news. call your local ATF office to find out for sure whether you can own a firearm. chances are, if you were not convicted you will be fine.
Unfortunately, you cannot buy a gun especially if you were arrested for a felony. It does not matter if you were charged or not. Firearms cannot be sold to people who have had a criminal record before.
Yes, you should be able to purchase a gun with an arrest on a felony charge. Believe it or not, even some convicted felons are able to legally purchase firearms. Some states permit (under their own state laws) the right to bare arms for felons after a certain time period. Federal laws are more strict on who and who cannot purchase firearms and should trump state laws, but they don't always do. There are a lot of if, ands, and buts when it comes to state and federal laws. That being said, it's actually pretty easy to buy firearms with or without a conviction.