Not that I don't believe you, but what kind of bullet would that be?

Well, technically they are called "expanding bullets" and they flatten on impact, effectively widening, making a much larger hole.

Oh, I see. You're talking about pretty much anything that's not FMJ. I was thinking that it was a literally exploding bullet. The smallest munition round that I know of is a 20mm. But my info could have been old.

No, they flatten in a unique way, unlike most bullets

The most devastating bullet that I can think of is a frangible round. I could understand how someone could think that they explode. It looks just like a normal bullet, but inside the brass jacket the lead is beaded, then compressed (not melted) together to form a very loose bullet shape. Now they're used by SWAT teams for clearing buildings where you might have civilians, because they won't penetrate more than one layer of drywall and still have the energy to kill.

There are also explosive rounds. The most powerful bullet in the world i believe is the 211 Raufoss or something like that, I think it has both a steel core penetrator and a explosive shaped charge for anti-material purposes.

Ah, so my facts are out of date, the smallest munitons round is in .50 cal. Fully half the size of a 20mm. An interesting round, but over priced for me. Lol.