From an e-mail conversation I had with an expert (wrote a book on exotic calibers and did some tests, but not all of them were in the book):
"Well I can tell you that the German / Czech steel core stuff and the M/39B is more effective against Kevlar than KTW is. Most of the KTW you find these days are the brass bullet type from when NAO was running KTW from 1980 to 1986. The steel bullet KTW stuff, like those still found in .357mag sometimes is a little more capable than the 9mm M/39B or German/Czech stuff.
Against steel plate, the German / Czech steel core stuff is much better than KTW brass, and sometimes better than KTW steel bullets depending on caliber. The M/39B does ok on thin steel plate, but nothing too thick, since it is just an inner steel cap, and not a hardened core.
The German & Czech steel core stuff (it's actually iron core) does surprisingly well and is more deadly & dangerous than KTW in most cases, which surprises a lot of people since it is so much cheaper and more common. The cartridge are usually not in good condition however due to their age and the hardness of the primers. So to make the German / Czech stuff usable in modern pistols, it often has to be reloaded with new components, and doing it at slight +p levels makes it all the better. For something ready to shoot and which is intended just for soft body armor or vehicle bodies, the M/39B is more than adequate and ready to shoot."
Also, this might interest you:
http://ammo.ar15.com/project/Ammo_Cross_Sections/index.htmAfter some research, I went with Czech ammo that I got off gunbroker.
