Archive for the 'AR-15s' Category

I thought readers might find some interest in this.

As a bullet is fired, the rifling in the barrel forces the bullet to spin. So, in a 1:8” twist, rate the bullet rotates one full turn every eight inches. In a 1:7” twist, the bullet rotates one turn in seven inches. The smaller the number, the faster the twist; you need to remember this.

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If a bullet spins too slowly, it cannot stabilize and won’t achieve either optimum velocity or accuracy. What occurs is called yaw. The bullet is unstable and does not hit the target with the tip of the bullet, but perhaps the side of the bullet.

I built a retro AR-15 with a 20” barrel and 1:12” twist and fired 77-gr. bullets that perfectly keyholed the target because the rifling couldn’t stabilize the longer, heavier bullet. So, the bullet hit the target sideways. Accuracy is horrible with heavy bullets in that rifle. With 55-gr. bullets, however, that retro rifle with a 1:12 twist shoots the black out of the target. Rifling can also be too fast and over-stabilize the bullet causing the bullet to fragment in flight and lose all effectiveness.

When Eugene Stoner developed the AR-15, the idea was to use lightweight bullets in the 45- to 55-gr. range through a 20” barrel. Barrels were rifled in a slow 1:12” twist rate, capable of stabilizing lightweight bullets but not heavier bullets. Fast forward a few decades, and .223 bullets have evolved in bullet style, bullet material and weight. Today 75- and 77-gr. .223 bullets are just as common as 55- to 62-gr. bullets. Twist rate is your clue on what weight bullets will perform optimally in your gun. Some shooters might not think twice about the twist rate in their barrel, but if they knew that could fine-tune their bullet performance they might pay closer attention.

Twist Rate Sweet Spot

Most AR-15 rifles and carbines produced today use rifling with a 1:8 twist rate. In my opinion, a twist rate of 1:8 is perfect for a general-purpose, 16” barrel AR since this twist offers versatility and can easily stabilize both light and heavy bullets. In fact, the sweet spot for 1:8 bores are bullets weighing from 62 to 77 grains.

In the 1980s, when the U.S. military moved to the M16A2 rifle and the 62-gr. M855 cartridge, it chose a 1:7 twist rate that has become the de facto rifling in all U.S. military rifles and carbines chambered in 5.56 NATO. The change had to do with the 1:7 twist rate stabilizing heavier 70- to 77-gr. bullets and the rifling’s ability to stabilize tracer rounds. The 1:7 twist can stabilize bullets weighing up to 90 grains.

I had an engineering professor who was fond of saying, “Test them like you use them”. So, to prove out the thesis, I sat down at the range bench with a stock, off-the-shelf Springfield Armory ATC with its 1:7 twist rate for heavy bullets and mounted with a Leupold Patrol 6HD 1-6x24mm scope. I used Nosler cartridges since they provide a wide assortment of bullet weights, bullet material and bullet types — from lightweights like the Expansion Tip 55-gr. lead-free ET rounds and the Ballistic Tip 55-gr. BTV, to Match Grade 70-gr. RDF (Reduced Drag Factor), and the lunker in the bunch Match Grade 77-gr. HPBT.

More, including test results, at the link.

Medical malpractice kills more people than all AR-15s combined. https://t.co/qhYdZVtR3G

— 🔫UR a Smart Ass, Carl🔫 (@Ur_a_Smartass_C) March 20, 2023

All Outdoor.

Ideal twist rates produce a gyroscopic factor between 1.5 and 2.0.

Factors between 1.0 and 1.3 are marginally stable, but they’re generally considered too slow. Factors between 2.1 and 2.9 are fast, but stable and accurate. Factors above 3.0 are suitable, but not ideal. Climbing above 4.0 may cause over-stabilization of the round being fired, which can harm accuracy. The optimal twist rates for 5.56 and .223 loads are:

• 45-gr Varminter: 1:12 twist
• 55-gr (M193): 1:9 twist
• 62-gr (M855): 1:8 twist
• 77-gr (Mk262): 1:8 twist
• 80-gr Sierra Match: 1:7 twist
• 90-gr Sierra Match: 1:7 twist

The way I read the table, 1:9 twist rate is good for just about anything up to 77 grains.  I wouldn’t shoot anything above that in 5.56mm anyway.  Heavier bullets than that need to be .224 Valkyrie, 6mm ARC or 6.5 Grendel.  I once thought that .224 Valkyrie was a flash in the pan, but occasionally I do see it at Academy and Cabella’s.  It’s also possible to pick it up via Ammoseek.

I don’t have anything in that caliber and would not.  I like the 6mm ARC too much to switch to something less effective and versatile.

Okay we’ve covered this before.

So there is yet another post about magazine springs and whether they should be replaced, and if so, when.  This is in the same theme I wrote about several years ago when there was another little flurry of articles and posts about this.  I’m going to cover this ground one time for everyone.

Metal creep is caused from slippage of crystalline structures along boundary planes, whether FCC, BCC, or whatever.  One reader writes that “springs don’t wear out from compression.”  This is along the same lines as most of the [mistaken and incorrect] articles I linked the last time I addressed this issue that claimed that stainless steel doesn’t creep below the yield limit.

Do you know any piano tuners?  I do.  Yea, they have to go back a few days later and retune because of metal creep.  But most piano wires are carbon steel under high stress.  What about stainless steel?

Do not make the claim that stainless steel (like SS304) doesn’t suffer creep below the yield limit and at low temperatures.  Yes … it … does  (“In all tests at applied stress/yield strength ratios above 0.73 some plastic deformation was recorded”).

No offense, but don’t try to be an engineer if you’re not one. If you make the claim that SS304 (I presume the material of most magazine springs) doesn’t suffer from metal creep, you’d be wrong, and then you’d also be answering the question the wrong way.

The right way to look at the question is one of whether the creep is significant.  It usually isn’t, and it is less significant than for carbon steel.  It’s also not significant for applied stress/yield strength ratios lower than what the authors tested.  Where your specific magazine spring falls in this data set is best determined by the designer, not me (I don’t have drawings or any other design information).

Stop saying that it’s only the compression / decompression cycle that puts wear on springs.  Stop it.  Just stop.  That’s not true.

It … is … not … true.

It’s true enough that the compression / decompression cycle is fatigue wear, but it’s also true that this means slippage of the crystalline structures just like metal creep.

Again, the question is whether this creep is important under the specific design circumstances or not, whether the specifications are challenged or not.  It’s not about whether creep will occur.  It does, and it will, even if undetectable by you.

I’m not saying here that it’s a bad idea to leave your buffer spring compressed.  I’m not saying that it’s a bad idea to leave your magazines full of rounds.  Don’t misunderstand what I’m asserting.  I’m not even asserting that Brownells was wrong in their conclusions, even if they didn’t do all of the necessary analysis to properly arrive at their conclusions.

I am asserting that the justification for whether you do or don’t leave springs compressed has nothing whatsoever to do with whether the spring undergoes a compression / decompression cycle while it’s in the configuration it’s in.

It has to do with a materials and structural engineering analysis that most people don’t do (and probably don’t need to do), and which Brownells didn’t do for the video above.

This may sound like a nit, but not to an engineer.

We’ve covered this before.  Softer metals can wear down harder metals if they make contact long and vigorously enough.  And he tells you so again in the video.

Travis Haley and Chris Costa go over height over bore very well in Art of the Tactical Carbine, but if you’ve never thought much about this or seen the series, this is a good explanation of what you should think about in CQB concerning the axis of the bore versus the axis of the optic.

Ammo.com has a lot of great articles. We’ve been following them on social media. You may find the Resistance Library interesting. On to the AR Calibers article:

5.56 Is Great, But…

Let’s be honest about one thing, the 5.56 NATO/223 Remington is a battle-proven cartridge that has valiantly served the US military for decades. The 5.56’s effectiveness is well documented, and it is one of, if not the, most popular centerfire rifle cartridges in North America.

Yes, the 5.56 NATO is awesome. It has low recoil, a flat trajectory, is inexpensive, and has more varieties of ammo than you can shake a boomstick at.

But sometimes you want to shoot something different out of your AR, and that’s ok. One of the greatest aspects of the AR-15 rifle is its versatility, as many caliber conversions can be accomplished with a simple upper receiver swap. However, with so many different rifle calibers available, some shooters might be confused as to which cartridge is best for their AR-15 or AR-10.

In this article, we are going to break down the top 13 best AR calibers that aren’t 5.56 NATO so you can understand which one will best suit your shooting needs.

If you can’t wait, the best AR caliber is .22 Long Rifle, however if you want to see the full AR caliber list then keep scrolling.”

The article breaks down; the best overall, home defense, long-range, varmint, hunting, and more. It’s well worth a look.

Just wow.  If this is the level of reasoning present in the courtrooms of American, it’s no wonder we are in such trouble.  The judges are just awful, especially Thacker (while Neimeyer and Richardson are only slightly better), and while Neimeyer and Richardson should probably be disallowed from doing anything more complicated than sweeping floors, I’m not certain that Thacker should even be allowed to answer phone calls.

I’m also not very impressed with the first attorney, but the second one (arguing for the state of Maryland for the AWB) was as dishonest as he was disrespectful of the judges.  He had the gall to argue that the fact that so many people own AR-15s didn’t mean that it was in common use for self defense.  He wanted the case to be remanded back to the district court to develop that argument (he doubts that it’s ever been used).

It’s astonishing that the judges didn’t hold him in contempt for making such a ridiculous argument.  Even after Bruen, the state of Maryland still cannot abide the ownership of America’s Rifle, and also cannot seem to come up with good arguments against it.  If the judges allow that bit of stupidity he expressed to hold the day, it’s a stupider court than I had even imagined.

And I’m very unimpressed with the 4th Circuit.  For what it’s worth, the entire edifice of whether a weapon was once in military use is silly and was never a good foundation.  All weapons were used in the military, pump action shotguns, semiautomatic shotguns, bolt action rifles, semiautomatic rifles, machine guns, cannon, knives, etc.

Listen to it all, or begin at 24 minutes if you want to hear someone actually argue that ownership of said weapon doesn’t count as common use if it hasn’t actually been used in a self defense scenario.  He wants you to suffer a home invasion in order to kill his argument in court.

Gun controllers are such awful people.

Source.

The writer has it at (5) Lee-Enfield, (4) AR-15/M-16, (3) Mauser Gewehr 98 / Karabiner 98k, (2) Mosin-Nagant, and (1) AK-47 and derivatives.

They don’t do much in the way of producing evidence for their assertions and I have my doubts.  For example, who is to know how they counted AR-15s/M-16s?  If you sum the total deployed to SE Asia, Iraq, Afghanistan, other armies across the globe, and AR-15 and variants, including upper and lower receivers sold separately, would you have come up with their number of 20 million?  I seriously doubt it.  I think there have been more than 20 million full ARs sold in America just in the civilian market alone.

However, it’s worth nothing that the gun that was built for conscripts (AK) who didn’t know how to shoot and didn’t want to mechanically understand the gun has been quite successful.

That’s one observation that should be made, of course, that genius Eugene Stoner designed his rifle for the professional soldier who needed MOA or sub-MOA performance, and wanted to understand how to work on his rifle.  As it is said, the AR is an MOA gun, while the AK is a minute-of-man gun.

Furthermore, America was built, at least up until the 1980s or so, with garage, backyard and farm mechanics working on cars, gun, and machines of all sorts, repairing them, cleaning them, and making them better.  Eugene Stoner knew this, I suspect, and didn’t worry too much that it was “too professional” of a rifle for the professional soldier.

From my point of view, Stoner understood the AK about as well as Kalashnikov did. Watch and tell me I’m wrong.

Here are the preceding two videos of Stoner and Kalashnikov at the range (Link 1 and Link 2).  One day I’ll embed the entire Eugene Stoner tape library for viewing.

We wonder if Herschel has made the pilgrimage to Stoner’s gravesite. OTOH, we probably shouldn’t joke about this; avoiding a pay cut from Herschel seems prudent right now.