Im not exactly sure what to call this weapon but heres what it could do.
I would shoot a special bullet something like a C4 bullet or something, when the player gets hit it would explode inside the player 3 secons after penetration. 3 second is for any friendlies to get out of the way as well as yourself. This weapon is kind of pointless but just the thought of exploding my opponent from the inside out seems exhilirating.
When the bullet hits a hard object (i.e door or wall) it would explode.
Advantages:
You know they will die
1 shot, many kills (possibility to kill by standers with explosion)
Inter changebility of automatic regular bullets and these C4 tipped bullets.
Disadvantages:
You could kill yourself shooting at close range
Weapon would plobably be better of as a addon mod to another weapon. Much like the nade laucher is.
A hero is no braver than any ordinary man, but is braver for five minutes longer.