How good is the magnum research baby desert eagle?

no it would not be accurate enough,(try it on paper with a good solid rest, bet you cant hit the same place twice) you would be better off getting a .177 benjamin pump pistol, they are very accurate and pack a little more punch then a ballisticly inefficient BB and they shoot a pellet through a barrel which is rifled, hence the accuracy. your Desert eagle just pushes the round ball(BB) down a smooth barrel, where as the pellet skirt and land on the pellet is engraved by the barrel lands and grooves which providing spin which also provides stability to the pellet