I too am adverse on both rounds, I have read an autopsy report on the 5.7 and witnessed an autopsy on the 5.56. The 5.56 will average 8” to 12” penetration with possible pass through, and create about a 4” to 6” hemorrhage. The 5.7 will create the same hemorrhage but with about 6” to 8” depth with no pass through. (From a p90). Out of 11 hits with the 5.56, two failed and passed through.Having followed the FN 5.7x28 since it was developed, I don't find it hard to believe. Another nonstarter is the 4.6x30 from HK. The original loadings used an aluminum core bullet, and I believe they've moved to plastic for the sharp nose "AP" loading. As such, you'll have no expansion. So, like I said, you have what's essentially a 22WMR, just with hugely better PR. FN has been pimping this thing hard since day one. Remember the Peru Embassy siezure? Purportedly, very early P90's were used there, why, I have no idea, but I have some ideas. Mostly revolving around the concept of getting to sell an entirely new weapons class and all it's accessories to a bunch of gullible(or flat out corrupt) REMF's in the DC area.
Having been involved with a fairly high number of shootings, involving everything from 9mm FMJ to 40mm HEDP, I do not find that story unbelievable. 5.56, a caliber with vastly greater performance, has been disappointing on several occasions IME. Bullet placement is critical, this is assumed, but I find no reason to handicap yourself with a marginal caliber like 5.6x28. S/F.....Ken M