Variable Yield Round

[Disclaimer: I know next to nothing about guns, as you can probably tell. I'm sure the better-educated will point out my mistakes.]

A conventional round starts with the primer, which is the bit that goes bang when the bit of gun hits it. This then makes the powder go bang, which makes the bit of metal go forwards really, really quickly.

There are centrefire rounds, where the bangy bit is in the middle, and rim-fire rounds, where the bangy bit is at the edge.

Let's make a round that's both centrefire and rimfire, with a metal tube dividing the bangy-powder into a central cylinder ignited by a centrefire primer, and an outer annulus ignited by a rimfire primer.

The annulus will contain more powder. Let's place the tube so that there's twice as much powder outside it as inside it.

Now, let's fire this round from a gun that has two hitty bits, one in the centre and one on the rim. Clearly, this means the bullet can achieve three different levels of quickly-going-forwardsness!