Archive for the 'AR-15s' Category

If you don’t do anything else today, watch this video entirely.  It’s well worth your time. There is also information presented by Stoner that doesn’t fit the narrative, so it’s a good history lesson.

Do you think it would have been fun to have worked with him? I do.

Reader =BCE56= links Ballistic Pressure Wave Contributions To Rapid Incapacitation In The Strasbourg Goat Tests.

Chamberlin observed damage remote from the wound channel he ascribed to the hydraulic reaction of body fluids [CHA66]. Tikka et al. showed that ballistic pressure waves originating in the thigh reach the abdomen. Wounding and delayed recovery of peripheral nerves have been reported [LDL45, PGM46]. Pressure waves cause compound action potentials in peripheral nerves [WES82], and ballistic pressure waves have been shown capable of breaking bones [MYR88].

This shows that, all other factors being equal, bullets that produce pressure waves of greater magnitude incapacitate more rapidly than bullets that produce smaller pressure waves. The Strasbourg test data convincingly supports the pressure wave hypothesis and allows (perhaps for the first time) the fast response time to be modeled as a function of peak pressure wave magnitude.

[ … ]

The trend in bullet design over the last decade has drifted toward bullets with little fragmentation and a higher percentage of retained mass. Bullets that both fragment and meet minimum penetration requirements create larger pressure wave magnitudes and offer improved incapacitation potential.

There is much more at the link.  I find it especially interesting that the authors use a 4*pi()*r^2 model for pressure wave solid angle (as with sound, light and radiation, unattenuated [or scattered] and unreflected).  The pressure wave isn’t forward peaked.

I often claim I have the best readers on the internet.  I really mean it.  This is a good example of that.

And this analysis goes to the heart of the design of the 5.56mm round, which is to induce a pressure wave due to high velocity (KE = 1/2 * m * v^2) and then fragment into shrapnel with multiple wound tracks.

Thanks to reader =BCE56= for that great read.

Remus notes something he calls astonishing.

I’ve seen a lot of pistol shootings, much more than US police would ever see, and much more than experienced by most medics deploying solely with US personnel. And yet, I have zero, not one single experience, where a single gunshot wound from a 9X19 NATO round killed someone prior to them being able to return fire or flee. This includes people shot in the chest, back, back of the head (one hit behind the left ear) the neck and the face. None…

Unfortunately, the same goes for the 5.56 NATO round. I have yet to witness a single shot quick kill with this round… On the flip side, having a patient who was shot by a 7.62X51 NATO or larger round was a rarity. Dead people aren’t patients, they are a supply issue.

That isn’t so much astonishing as it is just bizarre to me.  First of all, I dislike it when someone begins their post with bona fides.  The data is the data, the analysis is the analysis, regardless of your bona fides.

But then the claim makes no sense.  My youngest son had absolutely no complaints about his weaponry when he deployed to Iraq, not did he when he came home.  He was quite pleased with the lethality of the 5.56mm round in CQB and urban combat (MOUT).  He used both his SAW and an M4, and actually both during room clearing operations.

Then there is the issue of what we know about the lethality of the round even at distance.  Everyone recalls the video that made Travis Haley famous, and it’s worth watching again just to demonstrate that in the hands of a competent individual, the round can be lethal out to 600 yards or beyond.

Then there is this picture of an insurgent who was shot with a 5.56m round in Afghanistan at 200 meters.

You think he was able to mount a counterattack?

One final video demonstrates what the 5.56mm round is capable of in the hands of a qualified marksman.

Shooting Sports USA:

Custom barrel manufacturers like Obermeyer, Krieger, Lilja, Hart, Douglas, Schneider and other companies which go by the maker’s last name, are your best assurance of good quality. That’s not to say that other maker’s barrels―let’s call them “semi-custom”―don’t shoot as well, but it is to suggest a lower element of risk involved in your satisfaction. I think it’s wise to request a stainless steel barrel since they will, on average, shoot a little better for a little longer.

It would be nice if a materials engineer and/or a highly experienced gunsmith would weigh in on this, but that’s not my understanding.  My understanding (which might be flawed) is that a SS barrel will be more accurate out of the box, but that whereas another barrel might last for 25,000 rounds, a SS barrel will last for 15,000 rounds before needing to be replaced.  Again, if my understanding is wrong on this, it would be good to know it.

The chambering option that probably gets the most thought about and worry over is throating. Throating, let’s say here for simplicity, controls the distance of a bullet; bearing surface to the origin of the lands of the rifling. Almost always, a rifle shoots best when a bullet at least starts near the lands, if not on them. If the bullet has to travel through space before engaging the rifling, that’s called “jump,” and that’s an issue of concern. Since there is such a difference in comparing length of short range and long range bullets for this rifle, some compromise has to be met. Essentially, getting less jump for the shorter 68- to 77-grain bullets fired from magazine-length rounds means that the longer 80-grain bullets used at 600 yards will be seated more deeply into the case (which will reduce powder capacity). Short or long? Either, or anything in-between for that matter. It doesn’t really seem to matter. Why even talk about it? Why not? Everyone else does. What they’re not really talking about, though, is who’s shooting what scores with various ideologies. That’s because AR-15s shoot just as well at 200 and 300 yards with all the different “magazine” bullets, regardless of where those bullets are sitting with respect to distance from the lands. What matters to 600-yard performance is that the shooter knows how to experiment and adjust the amount of jump the 80-grain bullets have, and that discussion is for another article.

Someone care to elaborate what’s he’s talking about here?

I was doing some research on barrels and was a bit puzzled to find that so many top flight manufacturers (e.g., Daniel Defense, BCM, etc.) are still putting “government profile” barrels on their guns.  The best research I can find on why such a thing exists shows the idea to be extremely dumb.

Marine Lt. Col Dave Lutz was the program manager for the M16A2 project from 1980 to 1983. He was later the VP for Military Operations at Knights Armament Company. Some years ago he shared the story of the government profile barrel on AR-15.com.

It all started with a drop gauge test. The gauge wouldn’t pass through the bore, so the assumption was that the barrel was “bent.”

We (Marines) were replacing a lot of “bent” barrels that were determined to be “bent” because the Armorer’s Bore Drop Gauge would not freely pass through some barrels during Ordnance Inspections (LTI’s). So the Logisitcs people had “Barrels Bending” on their list of “M16A1” things to “Improve” right after listing “Handguards Breaking.”

AR-15 lore tells us that GIs were using their rifles as pry bars to open crates, and they were bending the barrels by the muzzle doing it. Another story tells us that aggressive bayonet drills were the source of bending. This is the one that Lt. Col Lutz ascribed to, at least somewhat.

We “experts” thought this bending was from rough handling like during bayonet drills, etc., as an absence of any mid-barrel handguard damage in these rifles made one assume the fulcrum of such bending was the bayonet lug. So we made that part of the barrel thicker because we did not want the excess weight of a full length heavy barrel.

The last line of that quote highlights something interesting. There was internal pressure to make the entire barrel thicker. The Marines have always prided themselves on their marksmanship skills. A lot of their techniques and choices of rifle components have origins in competition. The Marines were the driving factor in the adjustable rear sights of the M16A2 as well.

Lt. Col Lutz and his team realized that a heavy barrel all the way through was not a practical solution for a lightweight combat rifle like the M16. So they made only the front of the barrel thicker to increase strength.

In testing using the bayonet lug as a fulcrum, and applying calibrated mechanical pressure to the muzzle, the new barrel was about 9 times more resistant to bend and take a set than an M16A1 profile. So we went with this “improvement.”

With the problem solved, the new barrel design went into effect. Only later did the team realize the actual cause of the drop gauge failure was something entirely different.

However, soon after I started using a borescope with a video recorder and monitor to inspect “bent” barrels. What I found was a mound of bullet jacket material at their gas ports. This build up was caused by a burr left from drilling/reaming the gas port. This was where the Armorer’s Drop Gauge was getting stuck. When we removed this “mound”, the barrels would all pass the Drop Gauge.

Realizing that the “solution” they presented didn’t actually solve a problem, they tried to course correct. Colt listened, and even put out civilian M16A2 copies that still had the standard lightweight profile. But the government was already too far down the road. The new technical data package was already written and put into effect. There was no going back.

First, I question their testing of the resistance to bending of a “government profile” barrel.  They obviously never got real engineers involved in this problem.  The highest bending moment in a cantilever beam will be where it is pinned, which in this case will be at the receiver.  As best as I can tell, not only didn’t they solve a real problem, they didn’t even solve the pretend problem.

Second, engineering resources would have performed a failure mode and effects analysis of the problem.  A failure investigation team of engineers should have been commissioned, not a military team.

Third, if you believe the problem is that Soldiers or Marines are using their rifles to pry open boxes or crates, then teach them not to do that.  That’s stupid.  I remain unimpressed with folks who try to mistreat, abuse and beat up their guns only to complain when they don’t work.

The second law of thermodynamics says that entropy always increases.  Fatigue, metal lattice stretching and deformation, metal creep, rust, corrosion and a host of other problems will affect any machine.  I once read that someone complained that he had used the butt of his rifle as a hammer for tent stakes and other things, and thus wanted “Milspec” parts so they don’t break.

Listen to me.  Milspec isn’t better.  Milspec isn’t worse.  Milspec means that something was fabricated and built according to a specification, nothing more and nothing less.  Some guns and parts are better than Milspec, and some are worse.  Some are just different than Milspec because the buyer wants a different machine for a different purpose or with different parts simply because that’s what he wants.

The takeaway is this: don’t use your rifle butt as a hammer.  It isn’t a shovel, it isn’t a hammer, it isn’t a pry bar, and as for bayonet charges, you’re not going to do one.  Ever.  If you’re doing a bayonet charge, you failed to do whatever you needed to do to make it a stand-off fight.  Your rifle isn’t a spear.

And the top end AR-15 manufacturers need to get away from fabricating “government profile” barrels.  They’re dumb.

If you think I wrong or don’t know the full history of government profile barrels, you can weigh in with comments.

Recoil:

In addition, the top of the mount also incorporates the activation button for the light, providing natural and ergonomic access to the controls, especially for shooters who use a thumb-over grip on their rifle. Tap the switch to turn the light on or off, or hold it to activate momentary on mode. Double tapping the switch engages strobe mode. INFORCE says the light will output approximately 1,300 lumens.

That’s a lot of light.  I’m certain it would be blinding in the dark to an assailant, but the danger is that it’s so bright that it causes dysfunction even in the shooter due to light scattering from walls, ground, etc.  I’d want to see this in the dark myself before buying, although with electronic components there are no returns.  I do like the offset mount.

The INFORCE web site doesn’t show this product yet.  The alleged cost is in the neighborhood of $239, with a $100 switch.  I found the cost of the Surefire M622 (with switch) to be $429.  That’s up a bit from the last time I looked.

Washington Examiner:

David Hogg: “If you need an AR-15 to defend yourself you need more target practice because you’re a terrible shot.”

First of all, he’s a liar and doesn’t really believe this because he’s not advocating that the police be disarmed of long guns, and has never done so.  He just wants the state to have a monopoly on violence.  It’s always enlightening to run things like this through the grits mill in order to see the hypocrisy of their views.  If you advocate disarming people other than cops, then you’re just a communist.

Second, as for not needing an AR-15 to defend yourself, I think Mr. Stephen Bayezes would beg to differ when he used an AR-15 to defend against multiple assailants in a home invasion.  So would a number of other folks.

However, Hogg is right about one thing.  We all need more practice.  So let’s heed Hogg’s counsel and make sure not to neglect range day.  I think Jerry Miculek said in one video that he has shot somewhere around 7,000,000 rounds downrange in order to get as good as he is.  I know that my son shot well more than half a million rounds in his workup to deployment.

We’ve all got a little bit to go, I suspect.

Wirecutter has this video up on barrel twist rate.  Go to his place to see it.

I don’t think the author of the video understands the basic concept and what’s going on here.  This is a screen shot of the video I linked on barrel twist rate.

Bullet tractability is the degree to which the nose of the bullet follows the trajectory.  In the screen shot above, it doesn’t.  This can indeed happen if the bullet is overstabilized, something we concluded in our assessment of this.

In the video (screen shot above) it is explained that this doesn’t usually happen at closer distances, but rather towards the end of the flight path.  In the case of the 5.56mm flight path, we’re looking at around 500 yards effective distance.

The author of the video Wirecutter gave us is shooting at 100 yards.  Basically, I’m saying he has proven nothing at all.  He’s a decent shot, but he hasn’t tested what he thinks he has tested.

And by the way, the twist rate, if you’ll remember, of 1:7 was meant to stabilize the tracer round.  But most twist rates for common ammunition should be fine.  The testing conducted by the Army on both older and newer 5.56mm ammunition involved 1:8 accurized barrels.

Prior: AR-15 Ammunition And Barrel Twist Rates

See the list at Shooting Illustrated.  This one was particular interesting.

Alexander Arms Highlander
Available in 6.5 Grendel, .50 Beowulf, .300 BLK and .17 HMR, the Highlander offers the added efficiency of a carbine-length gas system in select models.

The .50 Beowulf is a large bear round.  I cannot imagine shooting that out of a pistol length barrel.  It’s interesting that they have engineered this down to the .17 HMR, which of course is a rimfire round.  I wonder about the reliability of cycling this round in an AR?