>>The powerful ones have such high muzzle velocities that the pellet is supersonic and it cracks like a regular rifle. <<
Tape straws to the sides of the barrel, then slip a condom over them and the front sight and it’ll quiet down considerably.
What is a “high powered BB gun”?
They sure a hell are not the good old “Red Ryder”, lever action BB guns we had a kids. Today’s versions (improperly named) are equal to more high powered .17 and .22 calibers used for hunting purposes. The are actually “pellet” guns (usually lead shaped projectiles)rather than the older, copper coated, round shaped “BB” guns of old.
Bubble wrap and the condom does a good job, too, if the straws are strong enough to keep the wrap tube cylindrical. Use five straws, usually.