A few articles about terminal performance of bullets from DOC GKR and others relating velocity and barrel length.- edited to pick out a few paragraphs. Velocity matters, unless you're just shooting paper.
https://www.itstactical.com/warcom/ammunition/military-ammunition-failures-and-solutions/ https://www.justice.gov.za/comm-mrk/exhibits/Exhibit-JJJ-112.pdf http://www.mlefiaa.org/files/ERPR/Terminal_Ballistic_Performance.pdf https://www.realcleardefense.com/ar...ich_service_had_the_better_bullet_114140.html "Criticism
There has been much criticism of the poor performance of the bullet on target, especially the
first-shot kill rate when the muzzle velocity of the firearms used and the downrange bullet
deceleration do not achieve the minimally required terminal velocity at the target to cause
fragmentation.[19] This wounding problem has been cited in incidents beginning in the first
Gulf war, Somalia, and in the current conflicts in Iraq and Afghanistan. In recent lab testing
of M855, it has been shown that the bullets do not fragment reliably or consistently from
round-to-round, displaying widely variable performance. In several cases, yawing did not
begin until 7–10 in of penetration. This was with all rounds coming from the same
manufacturer.[19] This lack of wounding capacity typically becomes an increasingly
significant issue as range increases (e.g., ranges over 50 m when using an M4 or 200 m when
using an M16) or when penetrating heavy clothing, but
this problem is compounded in
shorter-barreled weapons. The 14.5 inches (37 cm) barrel of the U.S. military's M4 carbine
generates considerably less initial velocity than the longer 20" barrel found on the M16, and
terminal performance can be a particular problem with the M4. Combat operations the past few months have again highlighted terminal performance
deficiencies with 5.56×45mm 62 gr. M855 FMJ. These problems have primarily been
manifested as inadequate incapacitation of enemy forces despite them being hit multiple times
by M855 bullets. These failures appear to be associated with the bullets exiting the body of
the enemy soldier without yawing or fragmenting.
This failure to yaw and fragment can be caused by reduced impact velocities as when fired
from short barrel weapons or when the range increases. It can also occur when the bullets pass
through only minimal tissue, such as a limb or the torso of a thin, small statured individual, as
the bullet may exit the body before it has a chance to yaw and fragment. "
"Unfortunately, combat operations since late 2001 have again highlighted terminal performance problems, generally manifested as failures to rapidly incapacitate opponents, during combat engagements when M855 62 gr “Green Tip” FMJ is fired from 5.56 mm rifles and carbines. This is not surprising,
since M855 was not originally intended for use in carbines or rifles, especially those with short barrels."
"This failure of 5.56 mm bullets to upset can be caused by reduced impact velocities when hitting targets at longer ranges, as well as by the decreased muzzle velocity when using short barrel carbines. Failure to upset can also occur when bullets pass through minimal tissue, such as a limb or the torso of a thin, small statured individual, as the bullet may exit the body before it has a chance to upset. Finally, bullet design and construction plays a major role in reliable bullet upset. Without consistent bullet upset, wounding effects are decreased, rapid incapacitation is unlikely, and enemy combatants may continue to pose a threat to friendly forces and innocent civilians."
"
These carbines had shorter barrels, usually around 14.5 or sixteen inches, which gave them lower muzzle velocity compared to the full twenty-inch barrel of the M16. The lower velocity of these carbines led to incidents such as those in Mogadishu where the M855 fired out of a CAR-15 failed to fragment and put targets down reliably. The issue of M855 lethality continued to plague the military in the post-9/11 era. As the wars in Iraq and Afghanistan dragged on, the U.S. Army and Marines began to issue out M4 Carbines, which use a 14.5-inch barrel, in larger numbers. This only exacerbated the problem with M855. "
Terminal Ballistic Performance of the 5.56mm Cartridge
"
If using a short-barreled weapon: The same guidelines apply as for barrier penetration loads. SBRs
usually have insufficient velocity to achieve fragmentation velocity."
I respectfully disagree with those claims, for the following reasons:
Every unit within JSOC and SOCOM started using shorter and shorter barrels after looking at all their AARs, formal ARDEC studies, and the pros and cons to barrel length. Even the USMC ditched their beloved 20” rifles in favor of Hk416/M27 IAR with 16” pipes, and MARSOC stayed in the SOCOM Block evolution approach with Block II and III with shorter barrels.
That old data about 5.56 performance has been so thoroughly debunked, I’m surprised to see it referenced in 2023.
We have a lot of data from 5.56 and 7.62 NATO performance even from early-on in GWOT, as well as large data studies done from Vietnam, Grenada, Panama, and Mogadishu. There are incidents were 7.62 NATO FMJ passed right through combatants at intermediate range, especially smaller trunk persons and healed-up as if they had never been shot. That isn’t the norm, but all of these cartridges are relatively small in bore diameter. They stacked enemy KIA like corkwood in Vietnam, Grenada, Panama, and Mogadishu with 10” to 14.5” barrels.
Grenada: Unit guys with Colt 653s (lightweight 14.5” barrels, guys with M203s have 20” M16A1s due to the lack of a 14.5” pencil barrel M203 combo, which was developed after Grenada for the Colt Commandos)
Panama, Colt 723s suppressed
Colt 723s with 14.5” barrel, Panama
Keep in mind that the units who saw the most combat in US history were Recon Teams in SOG out of Command and Control North. Their preferred weapon was the 11.5” XM177E2, colloquially referred to as the “CAR-15”.
There were no complaints of 5.56 terminal performance from those guys, or JSOC in the 1980s. Mark Bowden’s book,
Blackhawk Down, made a big deal of it from one person’s anecdotes he interviewed. Guys in JSOC analyzed the Command & Control bird video footage and narrowed-in on the most vocal person who complained about M855’s lack of performance in Mogadishu, and saw that he wasn't even making his hits. Paul Howe and Chuck Pressburg have discussed that and the 5.56 vs 7.62 NATO debate.
But the old M14/7.62 NATO proponents, feeling validated in the long-held assertions about 7.62 vs 5.56, started furiously generating articles in the gun rags about how 5.56 is ineffective, especially from short barrels, and we had a resurgence of the “poodle shooter” mantra in the gun community/military service rifle cartridge debate that sounded alarm bells of impending doom for soldiers equipped with 5.56 carbines. What is interesting is that the units who shoot the most and enjoyed more than satisfactory results with 5.56 did NOT have this reaction. In fact, they started using shorter and shorter barrels.
For the Recce carbines in those units, used on Sniper Operations Teams, they wanted more accurate barrels, free-float, and compact Variable power optics to complement their M14s and SR25s, which were sparsely employed in the mix using an Arms Room approach (end-users plan and select their weapons configurations per the mission). This is where the select match Douglas and Lilja special-order pipes were installed by Unit Armorers with free-floated handguards even before the emergence of the ARMS and KAC rails.
They were shooting a lot of 69gr Match in a light DM carbine set-up well before the development of the Mk.262 77gr SMK OTM. Sinister would be a better source to pipe in here on the specifics of that history.
This thread is about 12.5” 5.56 carbines, which really don’t lose much to 14.5” carbines. There are 2 main categories of use for a 12.5” or 14.5" carbine:
1. Close Quarters work
2. Short to intermediate work
For #1, it almost doesn’t matter what bullet you use for terminal effects. M855 will canoe heads, perforate chests, fragment bone, and you’re shooting rapid strings anyway. Reliability is #1 priority for a CQB/CQM blaster in that application. I would have zero reservations about using M855 in-close because it doesn’t matter. M193 is fine as well. The subsequent bonded and other enhanced terminal performance bullets that have been specifically designed to provide lower impact velocity expansion have been described as particularly effective as well.
You can deal with #2 using better bullets with higher BCs, like the 70gr RDF (.416 G1), 73gr ELD-M, 77gr TMK, or 77gr RDF, with a good magnified optic on top. I like the numbers and form factor with the new wave of higher BC .224 bullets that are meant to be mag-COL compliant in the AR-15. If I had a 12.5” in a DM set-up or dual-role, I would back the truck up on whichever shot the best for the availability and price point I could get them.
I personally shoot 6.5 Grendel from 12” regularly (was just doing it this past weekend day/night/day along with multiple 5.56 DMRs, 18” Grendels, .223 bolt gun, and .308 Win) and when you see and hear the impact of 6.5mm on steel vs anything .224” at distance, it’s a no-brainer. There was one particular moment when one shooter was firing his 22” .223 Bolt gun with 77gr at the same target being shot with 12” Grendel and 123gr as I was spotting. I saw the little nick made by the .223 and then the big splash from the Grendel, with a “tink-DING” audible feedback. It was kind of comical in the moment.
The biggest question someone looking at 12.5” barrel length needs to answer is whether they will be shooting suppressed or not. If suppressed, I’m a fan of the MLGS. Next biggest question is whether they are going to just be using it for close work, or some frequent intermediate range shooting from 200-600yds. That will drive optics and barrel quality/accuracy/ammunition preference.
For me, the puny low-energy impacts on steel with .223 (even up at higher altitudes where the air is thin and in your favor) don’t really do much for me, so I basically am invested in whatever 5.56 blasters I already have with no real incentive to get any more.
