Spartakis and others, it's nice to see people here mentioning the barrier blind loads, noticing the shift and also quoting DocGKR... I've been a huge advocate of barrier blind loads for quite some time and a big believer in TSX, especially the Black Hills 50gr which is different than the 50gr TSX bullet available separately and the 70gr for hunting and longer range applications.
I'm still a fan of 75gr TAP and also for long distances, Mk262. M855 is good stuff, but one of the drawbacks is the distance required for bullet upset... With TSX and TAP, we're looking at massive upset within a few inches, roughly 4". With 855, it can be as deep as 9" or so before upset begins. From the front, the center of the heart and the aorta are about 4" deep. So, certain OTM's and barrier blind loads will have massive upset near that point while others like 193 and 855 will not upset until far past. The thing is with TSX and TAP is the upset begins early but continues for a minimum of 14", depending on bullet choice.
Bringing SBR's into the conversation.... Before, we could expect reliable fragmentation or expansion from a 10.5" barrel to 15 yards, give or take with FMJ and maybe 25 or 30 with mk262. 75gr TAP in 5.56 quickly became the champ with an impressive 45 yards for maximum reliable fragmentation if it did not come in contact with a barrier. Barrier blind bullets were averaging about this same distance. On a side note, there's a certain person working for a firearms company that's on Lightfighter and m4c that had a couple confirmed kills with mk262 from a 10.3" barrel at distances around 350 meters, so it's obviously not only fragmentation or expansion that matters, but it's very important when the threat is close range and we need them to stop right now.
Now we have the TSX bullets. The newer Black Hills 50gr is geared towards LEO's where the average max distance will not exceed 200 yards and is likely to be much closer and around vehicles or other barriers. The 70gr also shines here, but the 50gr is slightly better at closer ranges. Keep in mind, barrier blind loads expand and do not fragment, so a 50gr bullet can be ideal while a 50gr OTM is certainly not ideal for more than varmints in most cases.
We see very consistent and reliable expansion to .5" from 50gr and 70gr TSX all the way out to 110 yards, more than double the previous champ, the 5.56 75gr TAP.
This is not to say 193 or 855 are not a good choice, as they are almost certainly better than any standard handgun ammunition choice, but there are much better choices out there.TSX is expensive. There are loads out there that cost 60% less with 90% of the performance. This is good for most. Personally, I keep a few mags of 50gr TSX and 75gr TAP T2 then a good number of extra mags filled with 855.
EDIT - Varmint loads are not the ideal choice for home defense loads. They often fail to penetrate deep enough and there are countless case studies of LEO's using these loads and even with good shot place,eat, they failed to stop the bad guy. OTM bullets are a much better choice for home defense of over penetration is a concern. Varmint loads should be used on varmints. Sure they're better than nothing, but they are at the bottom of the 5.56 ammo list, even below most FMJ.
For anyone wanting to know more about 193, there are two primary things to look into. First, Google Dr. Martin Fackler and m193 then Google Paul Howe, m193 and Mogadishu. He said the 193 zipped right through the people there often requiring a great number of hits before they went down. This has to do with what I mentioned earlier about neck length and how m193 might not even begin to upset until its close to exiting someone with a smaller frame.