Gun Control & RKBA

A gun launches a projectile of x weight at yvelocity with a kinetic energy of z.

It does not matter if the force used to launch the projectile is compressed air, as it a BB gun, or gas from burning gunpowder in a firearm. if you increase either the velocity or weight you get more energy i.e. the potential to cause more damage.

Most BB guns put out only a few foot pounds (ft/lb) of energy, they can break the skin but likely no life threatening injury
Hunting air weapons are more in the 20-30 (ft/lb) range. They can kill if they hit a vulnerable spot.
The .25 ACP, one of the weakest firearm cartridges, has around 65 ft/lb.
For comparison the 9mm has around 320 ft/lb and the .223 from an AR-15 is around 1175 ft/lb.
A .30-06 hunting rifle has 2900 ft/lbs give or take.

The Army considers 58 ft/lbs to be lethal although 53 ft/lbs can penetrate the skull.

You may think it is the velocity that makes firearms more deadly however good air guns can exceed 1000 feet per second which is as fast or greater than many pistols. It is the weight of the projectiles that firearms can push out. BBs weigh near 5gr, air gun pellets about 8gr. Firearm bullets vary for each caliber but for an average, a .25 ACP weighs 45gr and a 9mm 115gr.

That was a lot of words to say anything that has more impact is more likely to be lethal.

Unless you are prepared to risk killing someone in self-defense, I would suggest staying away from any solid projectile weapon.