[Clean_Sweep]

The 223 is not a super fast round compared to other 222 centerfire calibres. The tumbling effect of military ammo was a way to work around the Geneva conventions which do not allow spire (normal hunting ammo which mushrooms) ammo in war. A hunting round would cause more trauma than a tumbling bullet and that's probably what these guys are using.

Military ammo does not tumble, it never did because of bullet design anyway. In the early use of the M16 there was a barrel fouling problem due to the type of ball powder. Tumble within a target happens due to density changes in the target, things like bone alter the direction of travel.
3000 fps from a 223 is plenty fast and faster than most. You will have a hard time pushing any 30.cal round that high unless you have a belted cartridge like a 300 Win. Mag.

[Myrddin]

The tumbling effect was caused by the inadequate stabilization of the 1:14 rifling used in the initial M-16. The current issue uses 1:7 rifling to stabilize a typical 62 to 69 grain round. The 1:7 rifling overstabilizes a 55 gr round pushed to 3150 fps. The guilding can spin off and bullet disintegrate. A 1:9 rifling is just about optimal for .223.

[epow]

You will have a hard time pushing any 30.cal round that high unless you have a belted cartridge like a 300 Win. Mag.

A friend of mine does it easily with measley little .308 cases handloaded with 110 grain HP bullets. Not a terribly accurate load, but it makes a real mess out of ground squirrels if you can hit them. I've gotten over 2700 fps out of my 26" bbl .30-30 loaded with 100 grain Plinkers and the old Hercules RE7 powder. There's not many uses for that load and rifle combination though, so I usually load 150 gr Core-Locs to around 2300-2400fps with a slower powder.