Not really, no.
In fact, some more recent work suggests that some heavier, lower velocity rounds are superior in terms of wound ballistics. Current tests of newer, magazine sized 75, 77, 87 and even 100 grain rounds show faster yaw in ballistic gel and much more dramatic fragmentation than M855. Some 75gr open-tip (i.e., JHP) match bullets have performed very well in law enforcement use over the past 5 years or so. Additionally, 77gr open tip match bullets seem to be performing very well for the US military in combat operations since September 11th. Also showing great promise is the 87 gr P.R.L. match round.
Some of these heavier bullets, probably because of their length, maintain their fragmentation down to below 2100 fps and as a result have a much longer range of fragmentation, out to as far as 300 yards.
The flip side is that these heavier bullets will require at least 1 in 7" twists for proper stability, are more expensive than 55 gr. FMJ, and some types aren't widely available as of this writing.
Some of the heavier bullets can offer superior performance, but at an increased cost. In the meantime M193 is probably still your best bet for bulk defensive ammo. Do take note: this does not mean that all heavy rounds are good terminal performers. Bullet construction is far more important than pure weight or velocity.
Perhaps most promising, however, is the 77 grain Nosler NATO loading from Black Hills. (Not to be confused with the 77 grain Sierra Match King which has a longer neck). This particular round has a very short neck, high fragmentation and wonderful muzzle velocity.
Some reputable testers have described the Black Hills 100 gr. round as the "most impressive performing .223 round we have ever tested." Unfortunately, despite excellent close-range performance, this experimental bullet was dropped due to concerns of over-pressure loads and "rainbow-like" trajectories at ranges beyond 100m.
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