.40 S&W and .357 Sig saw their heyday come and go. 45 GAP had a decent law enforcement following for a while but that seems to be waning as well. .22 TCM never really took off nor did 5.7x28 (as a pistol round). Yes some shooters still favor these calibers but the pistol market appears to have shifted back to 9mm and 45 ACP with some .380 thrown in for good measure. So how long before the next magic cartridge becomes all the rage and what do you suppose that round will be?