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benEzra

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Gender: Male
Hometown: Eastern North Carolina
Home country: United States
Current location: Eastern NC
Member since: Wed Dec 1, 2004, 03:09 PM
Number of posts: 11,607

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It's not that pressures are different (they are the same), it's the way the leade is cut.

The chamber profile, but not the max pressure, is slightly different in the two specs.

http://ballistictools.com/articles/5.56-vs-.223-myths-and-facts.php

CIP is the European version of SAAMI, they define the specifications for cartridges, including maximum pressures. Except that they don't use the same method as SAAMI. SAAMI measures pressure using a piston on top of an intact brass casing (called the "conformal piston" method). CIP uses a hole drilled through the chamber wall and the brass, exposing the sensor to hot gasses directly. NATO (outside the US) uses CIP's method when they define pressures.

When you measure a 5.56 cartridge that rates 55,000 PSI under the SAAMI method using the CIP method, you get somewhere around 62,000 PSI instead. Same cartridge, same pressure, same chamber, just two entirely different methods of reading the pressure. NATO uses the CIP method, so their documents will reflect the higher number, even though the specified pressure is the same.

You can prove this to yourself by checking out MIL-C-9963F and MIL-C-63989A(AR), the older US specification documents for 55gr and 62gr 5.56 NATO ammunition. Both of them specifiy a maximum average pressure of 55,000 PSI, along with the full velocities that 5.56 NATO is rated for. They aren't specifying a reduced power load for our military, they are correctly specfying the unit as measured with a test method similar to SAAMI's.

Another telling piece of evidence is that CIP specifies 62,000 PSI for both 5.56 and 223 remington, measured using their test method. This isn't some case of European ammo being hotter, unlike some calibers, there are no .223 remington antique guns that were not designed for the full pressure.


Here is the difference between a SAAMI .223 spec chamber and a NATO 5.56x45mm spec chamber:



The leade is longer in the 5.56x45mm spec, allowing the bullet to exit the case and get more of a running start before being engraved by the rifling, allowing the pressure to drop a little. Meaning that a load tailored for a 5.56x45mm chamber can use a tiny bit more powder while maintaining the same peak pressure (55,000 psi/62,000 CIP), resulting in a smidgen more velocity if the manufacturer tailors the load for a 5.56mm chamber.

Generally speaking, relatively few guns, even those marked .223, use true .223 chambers; a lot use a hybrid chamber like .223 Wylde that offers some of the theoretical accuracy benefits of SAAMI .223 without the potential overpressure problems if you fire an at-the-pressure-limit 5.56mm load in a .223 chamber at the lower bound of .223 tolerances. For example, my Ruger Mini-14 was marked ".223 Remington" on the barrel, but all mini-14's except the heavy barrel Target model had the NATO leade.

http://7.62x54r.net/MosinID/MosinHumor.htm

As a current AR- and Mosin- owner and a former AK owner, I laughed out loud...

Yes, exactly.

Which means that as I said, a .223 pistol kicks approximately like a 7.62x39mm (.30 caliber AK/SKS round) out of a rifle or a .243, except that the AR "pistol" will lift and rotate more in recoil due to the lack of shoulder/cheek weld and lower moment of rotational inertia.

BTW, that 75gr .243 has twice the powder behind it as .223 and is going 3400 ft/sec, compared to a 75gr out of a .223 which is only going ~2600-2700 ft/sec, depending on barrel length. The .243 is a .308 Winchester (7.62x51mm NATO) firing smaller bullets at much higher velocity than .308. The 75-grain .243 loads are about 200 ft/sec faster than a 55gr .223, and will handily penetrate things that M855 can't, out of the same length barrel.

Well...

"ezra: But since the First Rule of Gun Control Advocacy is apparently "If any restriction on gun owners comes along, no matter how pointless or counterproductive, it must be enacted at all costs", the ban-M855 circus must go on. Even though Bloomberg's own gun-control groups say it's not a ban they advocate..

You realize, ezra, you contradicted yourself in the above sentence."

Ummm, you and the gun control advocates in the media and Congress *are* advocating to ban M855, even though it has less ability to penetrate police armor than plain 55gr FMJ, and the gun control caucus in Congress has introduced at least two bills to make possession of it a crime. One even goes so far as to ban any ammunition that can penetrate a vest not designed to stop rifle ammo, which is downright silly. Bloomberg is distancing himself and his organizations from it, but gun control advocates in general don't seem to be.

"We often concentrate on the most extreme forms of firearms & ammunition."

Uh-huh. That's why you are fighting tooth and nail to outlaw centerfire .22's that are among the least misused weapons in the whole damn country, and slow ammo that penetrates less than faster lightweight pure-lead-core, and less than most deer rifles.

"This reminds me - you, & nobody else either, has answered of what use are these greentips? or ar15s? what are they good for in American communities? I know you enjoy target shooting but that is no reason to allow extreme ammunition to filter into communities (gun control would be merely hindering the supply), where they could be used to down planes & helicopters & penetrate cars, firing several accurate shots where higher recoil rifles could not, due to rifle rise."

Ummm...

(1) I've answered several times what use "these greentips" with the Scary Green Paint of Death are. Namely, inexpensive paper-punching at ranges beyond 200 yards, especially in rifles zeroed for slower, heavier bullets with high ballistic coefficients. That's what they're primarily used for, because they are certainly less effective for defensive purposes or for shooting through hard cover than 55gr or 77gr are.

(2) "extreme ammunition" that won't even penetrate Level III plate out of a 22" barrel at point blank range, when ordinary 55gr lead-core you can buy at Walmart will?

(3) "where they could be used to down planes & helicopters" --- seriously? What centerfire rifle caliber won't penetrate light plexiglas or thin-gauge aluminum? Heck, a .22LR will.

(4) "penetrate cars" - Actually, M855, and .223 in general, is relatively lousy at shooting through regular car doors and windshields compared to heavier calibers, which is one big reason M855 is being ditched by the military in favor of barrier-blind rounds like SOST, Mk 262, and M855A1.

"Also, ar15s account for relatively few of the yearly gun deaths & crimes, but they also account for relatively few defensive gun uses, especially legally shooting in defense. So what good are they for? when a safer alternative would do?"

How is an AR-15 less "safe" than a 9mm pistol? The AR-15 penetrates less, is less concealable, and is vastly less likely to be misused. I'll remind you that the worst mass shooting in U.S. history was carried out with an ordinary 9mm and a backpack full of non-extended 10- and 15-round magazines.

"While they may account for few illicit uses now, over the course of the next few decades they will become more hazardous.
Over the course of approx. a handguns lifetime (~2 human generations), approx. 10% to 15% of existing handguns will be used in a crime. Perhaps 30% will be used illicitly."

Uh-huh. How are 2-foot-long pseudo-rifles going to suddenly become as concealable as a 5"x7" 9mm? And how are they going to penetrate Level III armor with those stubby barrels, especially shooting slower, less-penetrative-at-close-range ammunition like M855?

"Answer me this: you are driving a windowless army jeep, armor plated with 1/4 inch steel. You can take one of two routes to get where you need to get. First is a 10 mile stretch thru rough roads, patrolled by isis guerrillas armed only with ar15's shooting 62 gr rem .223s. The other route is a very similar 10 miles stretch over rough roads, but patrolled by isis guerrillas armed only with ar15's shooting greentips.
Which route would you want to pass thru, which would provide the best chance of getting thru with less damage to the jeep & less injury to yourself? (sorry, you can't shoot back in this scenario)."

If you're talking about 1/4" steel armor, that's probably Level III rated, meaning 55gr M193 will penetrate it but M855 will not even at close range. So I'd be glad that the hypothetical morons were using 62gr that won't get through, instead of 55gr that might. I'd be especially glad that they bought the hype about non-AP green tip instead of simply procuring black tip AP that will penetrate 1/4" steel armor at several hundred yards, or 1/2" steel at 100 yards...

And of course, out of an AR pistol, M855 wouldn't penetrate even if your hypothetical assailant walked right up to the jeep and fired with the muzzle pressed directly against the armor.

INTERESTING. I just learned that 55gr lead-core FMJ (but ironically not 62gr M855)

can penetrate some thinnish AR500 steel armor rated NIJ III at very close range if fired out of a hunting length barrel; the test below is from a 22" barreled bolt-action .223 varmint rifle pushing the 55-grain FMJ at about 3240 ft/sec. To reiterate, this is plain lead-core copper-jacketed target-style ammo, not M855.



Ironically, the guy also fired a "green tip" M855 round out of the same rifle at the same distance at the same plate, and it did *not* penetrate even with the extra velocity from the 22" barrel.

So it looks like a 20" to 24" barrel can push a 55-grain lead core FMJ (but not 62gr M855) fast enough to penetrate a thin plate of AR500. That's interesting. I've pointed out before that M193 lead-core FMJ penetrates hard cover better than M855 at close range, but I had no idea M193 would penetrate actual III-rated AR500. Apparently even M193 is stopped if the distance is more than a few yards, though, as the relatively draggy bullet loses velocity quickly from aerodynamic drag.

So basically, from a hunting-rifle-length barrel, you get hunting-rifle penetration, but only with the light-for-caliber loads; M855 is too slow to penetrate even from long barrels.

That means that a lot of light-for-caliber .243, .270, .308, .30-06 non-AP hunting/varmint/target loads will likely penetrate NIJ III as well, if fired from hunting-length barrels. It also means that from an officer safety standpoint, redefining the NIJ III standard to what is sometimes called the "III+" standard would be a really good idea for those rare instances where officers face a perpetrator armed with a rifle at close range. Making III+ the default standard for rifle-resistant armor would mean that such armor could be counted on to stop multiple .223 through .308 rounds even at across-the-room distances from hunting-length barrels, whereas the current standard might let a light-for-caliber .223, .243, or .308 varmint round slip through from a long enough barrel if fired from across a room.

It also goes to show that M855 from a pistol-length barrel isn't really a threat as far as penetration of NIJ III armor goes; out of a 7-8" pistol barrel, M855 is barely going 1900 ft/sec, and out of a longer pistol barrel it might hit 2300-2600 ft/sec, whereas in this video it didn't even penetrate a level III plate out of a 22" barrel going ~3000 ft/sec.

I saw another video where a guy shot the same NIJ III-rated AR500 plate 60+ times with M855 green-tip, including multiple hits in the same holes, before the plate finally eroded/fatigued enough to start letting rounds through; this was from what looked like an 18" barrel at ~35 yards, which would be a decent stand-in for a 16" rifle or a long-ish "pistol" at point blank range.

Such as?

Again, M855 doesn't penetrate body armor any more than other small- and intermediate-caliber rifle ammunition does, AFAIK it's never been used to murder a police officer through the vest and is no more likely to be than any other small rifle round, and it is stopped by even the lowest level of rifle-resistant armor out there. What I see is a bunch of hand-waving that M855 is AP even though it's not, and some pretty silly assertions about how concealable and shootable stockless AR pistols are in dynamic situations.

M855 is no more a threat to police or the public than any other rifle ammunition is, and is less lethal than most. I don't see either of those statements as refutable.

And to address one new point he brings up in the above post:

"From 1986 to 2011, the agency received "very few" exemption requests, Seward said. But it has received 30 requests since then. "

I suspect that requests for exemption have been increasing because companies have been looking to create boutique lead-free alternatives to traditional ammo (the Army just went down this road with M855A1) just as the BATFE has been stretching the statute to cover more and more rifle ammunition. Unfortunately, most of the realistic alternatives to lead-core rifle ammunition fall under the AP bullet ban, even if they don't make a difference in penetration. Right now the gun control lobby in the odd position of saying that ammo containing lead should be banned because lead, and ammo containing anything other than lead should be banned because it's AP. The skeptical side of me thinks that may be deliberate.

This still doesn't excuse the BATFE jumping the shark and trying to ban lead-core M855, though, since it is clearly exempted by its majority lead content, isn't AP, and isn't a safety/crime issue, and this whole brouhaha certainly has me rethinking my prior support of the current AP bullet ban.

The only person angry in this thread is you.

The ATF made the right decision in pulling the proposal, for the reasons I outlined in the OP. M855 is no more dangerous than any other .223, or .243, or .308 (and semiauto range-toy "pistols" exist in those calibers too, JSYK).

And this particular contention is *ludicrous*.

"I then countered that with rapid fire ability, due relatively low recoil of a handgun firing greentips at a fixed spot, a couple could penetrate level III in same spot. And, how other rifles with higher recoil - gained by heavier bullets - could not penetrate level III bpvs by concentrating fire on one spot, due to rifle rise. "

A stockless .223 "pistol" recoils considerably more than a full-length AR, and is considerably harder to aim. Less mass, less moment of rotational inertia, no shoulder-and-cheek weld, more wobble, more difficulty in tracking the dot from shot to shot.

Blathering about drawing from concealment and putting several rounds in one hole in a second using a shorty AR "pistol" is like talking about shooting an Olympic-level skeet score with a stockless short-barreled PGO shotgun. Not. Gonna. Happen. Even Jerry Fricking Miculek can't do that. And anyone who *could* somehow do that could just shoot their intended victim in an unarmored region instead, much faster. If you can shoot 0.25-sec splits while hitting a dime-sized target with an AR pistol, how fast are your splits on an 8" paper plate at the same distance?

If you can do that, you should quit your day job and go kick everyone else's ass in every top-level practical shooting competition in the world.

Because M855 is lead-core *NON* AP, and if it can be designated AP under the new framework

then pretty much any full metal jacketed .223, or .243, or .308 rifle ammunition can be designated AP using the same framework.

I've been OK with the AP ban since it was passed in the 1980s, as I've pointed out here on DU since 2004 (and 5.56mm AP is indeed banned by that law, as I'm sure you know). But extending the AP ban to cover lead-core non-AP, even though the statute explicitly *excludes* lead-core ammo, turns the ban on its head.

To quote the law verbatim (18 U.S.C. § 921(a)(17)(B)):

(B) The term “armor piercing ammunition” means—

(i) a projectile or projectile core which may be used in a handgun and which is constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium; or

(ii) a full jacketed projectile larger than .22 caliber designed and intended for use in a handgun and whose jacket has a weight of more than 25 percent of the total weight of the projectile.


The "framework" document that ATF has since withdrawn would have gutted § 921(a)(17)(B)(ii) by pretending it applied only to rimfires under 40 grains, in contravention of the statute, and ignoring the "designed and intended for use in a handgun" language. More of a problem though is pretending that the "core...constructed entirely" language doesn't exist, because that opens the door to ban inexpensive bimetal-jacketed 55gr .223 range ammo, or plain 55gr M193 FMJ since it penetrates body armor as well as M855, or any FMJ up through .308 for that matter, including steel-jacketed 7.62x51mm.

The Dems who wrote this law wrote it to ban handgun ammo that would allow a .38 or 9mm to penetrate like a rifle round, not to ban rifle rounds, and they were insistent that it would and could never be stretched to ban rifle ammo (including M855 ball, which was on the market and which the law was worded to exempt). Gun owners didn't complain too much when it was stretched to include 5.56mm AP (M995) and 7.62x51mm AP, and we didn't even complain a lot when 5.45mm 7N6 was banned, but going after popular lead-core ball in .223 was a first-order shark jump.

As to the green tip, M855 ball is painted green to allow it to be distinguished from older 55gr M193 ball, because the old pre-A2 M16's had a slow 1:12" twist barrel and didn't stabilize the longer 62-grain loads very well resulting in poor accuracy. But it is ball (green tip), not AP (black tip).

Because they see it as caving to people they utterly despise.

Regardless of the merits, or lack thereof, of any particular gun control proposal with regards to addressing criminal violence, there seems one and only one heuristic determining whether or not to support it, and that is whether or not it goes after lawful owners.

Something that targets gun misuse *without* also targeting lawful owners tends to get a whole lot less support than something that targets lawful owners without addressing gun misuse at all. Compare the level of advocacy for prosecuting straw purchasers, or enhanced sentencing for career violent criminals who use guns in the commission of crimes, vs. the advocacy for banning the lawful ownership/use of big target rifles, or M855 non-AP .223, or legislating rifle handgrip shape, or harassing people with carry licenses.

Pointing out facts is always "rabid gun zealotry" if those facts

happen to run counter to any proposal that attacks peaceable gun owners. Even if the benefit (as in this case) is demonstrably zero lives saved. Even if the bans in question are based on fundamental misunderstandings of armor specifications, bullet construction, and Federal firearms law. Even if entirely imaginary and demonstrably ludicrous scenarios are invoked as their rationale.

If a ban cannot be supported based on facts (number of officers killed annually with M855, penetration ability of M855 vs. other common rifle bullets, whether or not M855's core is "constructed entirely" of steel vs. being made mostly of lead), then make stuff up. If these made-up scenarios (magic pseudo-SBR's that don't recoil, magic shooters who can hit a dime several times in a second with a stockless pseudo-rifle but who can't shoot for shit otherwise, imaginary bullpup .223's not much bigger than a longslide 9mm) still don't support the ban, then accuse nonsupporters of being insane, sexually deviant, or evil.

And at the end of the day, if the Federal agency that proposed the ban says "hmmmm, maybe we need to reconsider this" and pulls back, stick your fingers in your ears and pretend this had nothing to do with any flaws in the ban. Because any proposal that restricts the rights of gun owners must be righteous and justifiable and must be defended at any cost.



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