This would vary from state to state. Moreover, no matter what state you are in you would need to have more information to make a determination. But generally speaking it would not be.
Actually, it's difficult to say that it "would not be," even generally. In the U.S. the general definition of deadly force is "any type of degree of force that can cause death or serious bodily injury, including loss of use of a limb or organ." Shooting someone with a BB gun can (not saying it does always, just saying it can) fall into that category. Deadly force is one of the things used to determine whether assault is just simple assault or aggravted assault.