As was mentioned previously, the Mk318 was designed to essentially have the front half of the bullet fragment violently while the rear half punched on through for some penetration.

I've not heard the cartridge bad-mouthed. The M855A1 is it's closest military-issued rival, and opinions vary on which takes top spot. Of course the M855A1 has a good deal more chamber pressure driving it (as well as accelerated parts wear).

I think the M855A1 (if you can find it and it will cost $$$) is the only choice these days as the Mk318 isn't manufactured anymore. I'm glad I snagged what I could.