I would say the shape of the round and fps. They can be very accurate. Just look at the competition shooters, they are perty darn'd good. Those can get pretty pricey$$$$ I bought a Sheridan blue streak back in 1972.
It is an excellent air rifle. If you are planning on getting one. I don't believe you could go wrong. btw-Benjamin puts out a good quality gun too.
The main thing to remember when comparing any air rifle to .22 rimfire is that although velocities may look similar,projectile weight is vastly different-A LOT higher for the powder driven version,which of course affects energy level.
Air rifles has came a long way however,especially with the pressurized tank models.