It's 65% more bullet per bullet!

The Lord works in mysterious ways

It's not painted as a casing, more like an exceptionally extended body. It rather looks like a tracer projectile body. I suspect somebody searched for 5.56mm projectile references and picked the tracer at random.

The crimp mark is quite far up though, rather than on the major diameter.

Not every bullet has to be circumcised :(

If you’re cold, they’re cold