[stuartcr]

I think, with a round as popular as the .223, and the fact that it pretty much disintegrates at impact, ballistics could probably figure out the caliber, but to get any rifling off of it, would be very difficult. Besides, new, mass produced, military weapons, have pretty much the same signature.

[Shooter 2.5]

The intact bullets all point to one firearm. Until they found the empty case, they didn't know what round it was. At the beginning, all they had was a .224 bullet that fits eleven different cartridges. When they found the piece of brass, they started to report that it was a military round. The only military round that takes a .224 bullet is a military 5.56/civilian .223 Remington. They have not reported if there were any markings on the case that narrow down the type of firearm and whether it's a pistol, bolt action or semi-auto rifle.

[El Gato]

fact that it pretty much disintegrates at impact

But it doesn't. It ususally breaks into two large pieces, plus some very small fragments, plus the jacket peals off. .22 caliber centerfires with more powder behind them will do as you indicate, but not the .223.