Here's a harmless little Air-rifle "the Condor" will shoot the 14.3-grain .22 Crosman Premier at velocities of around 1,250 f.p.s. for the first five shots! The first 15 shots will usually be faster than 1,200 f.p.s., and even shot 20 will usually still be above 1,175.
That just might be a little mischievous for a kid's BB gun.
here's a harmless little bb-gun pistol that put out a round at about 1000 fps.