The Speer 50gr TNT bullets have been around for some time now. Wes is right on in his above.
I used them quite a few years ago to kill woodchucks coming out of an older 14" T/C Contender pistol chambered in 223Rem. They were explosive even at those vels. At 220Swift vels they will come apart if you hit a single blade of grass.
They are perfect for a 223/5.56. They will hold together even with a 1:7 twist.
Anyone remember the old Hornady 50gr SX (Super Explosive) ?? --- SAWMAN