Skip to comments.What about that AR-15..??
Posted on 10/20/2010 8:07:51 PM PDT by Bean Counter
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Went to bed last night so maybe this got answered already- 5.56 Nato has a different “lede” or I would say freebore beyond the tip of the chambered round; a longer one which allows barrel pressures around 70,000 copper units. .223 Remington is smaller, rated for around 45-50 cup, don’t recall exactly. You can overpressure a .223 chamber with a NATO round, but not vice versa. You give up a slight amount of accuracy shooting .223 thru a 5.56 barrel. External cartridge dimensions are the same- I think NATO is thicker in the base internally.
Most commercial semi-autos are chambered 5.56 ( Mini-14, etc.) Some bolt actions are not so you have to be careful what you put thru them, especially overall cartridge length if reloading.
Because there are alot of AR shooters after super-accuracy (varminters, especially)they offer the .223 chambering.
The dimension that matters most is the Freebore Length, ‘N’. They’re not the same, either on your chamber diagram or on others I’ve seen. The NATO freebore, or “Leade” is longer in the NATO chamber than the .223, and this is where the crap can hit the fan.
NATO ammo can assume that there is more freebore, which means that they can use ammo with longer bullets.
Put a cartridge with a longer bullet or longer OAL into a .223 chamber and if the bullet seats into the lands, the pressure goes way up in a hurry... and that’s where the serious problems will start. There’s nothing wrong with a bullet touching the lands, PROVIDED you make allowances for this situation.
eg, Benchrest shooters sometimes set up their chambers so the bullet is touching the lands while in the case, but they reduce their loads to account for this.
A conventional loaded cartridge that does not give the bullet any room to start moving before contacting the lands (even as little as three to five thou) is going to see the case pressures go above what you’re expecting. Possibly way above what you’re expecting.
Here’s a comparison of various reamers from different reamer sources and chambers based off the chart you posted:
Now, complicating the situation further is the issue of what the loading specs for the two cartridges specify as max pressure in a nominal load. The .223 Remington is SAAMI spec’ed to max pressure at 55,000 psi pressure, whereas the NATO 5.56 is spec’d to have a max average pressure of 58,000+ psi. In the case of “+ psi” I have seen data that shows some NATO loads running pressures up to 60,000 PSI.
Typical brass cases in a properly headspaced chamber should be able to support 60,000 PSI - they’ll probably start showing signs of pressure (flattened primers, etc). However, most brass cases start to fail at about 70,000 PSI. What is happening with the NATO ammo is you’re losing your margin of safety to prevent a case failure by how hot they’re loaded. Add in the sudden increase in pressure brought about by a bullet being pushed into the rifling from insufficient freebore, and you can see how putting a NATO 5.56 round in a .223 chamber could result in a case failure (and possibly worse).
Thanks for the clarification!
I gotta second post #11. (Did post in my sleep under a different handle? LOL) That said, I own only one Saiga, the semi-auto 12, and it rocks.
As to the rifle, I do own an AR. No complaints for what it is but I wish I’d gotten a beafier caliber than the 5.56. 7.62x39, .308, whatever and then ability to switch to cheaper-shooting upper if desired. .22 uppers? No problem. You can even get an upper to shoot the PS90 rounds - talk about your low profiles!
If you pick an AR, skip the front-sight gas block & carry handle. A decent holosight is fine. Check previous banglist threads for recommends. Within the past month there WAS one about that very thing, I think. If you insist, you can add BUIS and a carry handle to your rails.
Is that a new belly girl? LOL
see post #78
That’s expert marksman (woman) Bambi
I see a lot about the twist rate in terms of accuracy....sure, a stable bullet will squeeze out the most a system is capable of, accuracy-wise, but when you're talking about a 16 in. barrel, would not there be some advantage in having a round that is just waiting for an excuse to tumble like crazy? Never heard of any ballistic gelatin tests to confirm, but it seems the terminal ballistics of, say a 1:9 twist rate and a 62 gr. or heavier bullet would be pretty ferocious.
You're quite correct. And the older M16A1 1:12 twist barrels are not only also better at stabilizing the 55-grain bullets of the older military M193 ball load, but also work MUCH better with the various .22 conversion kits if lead-bullet .22 long rifle ammo is used.
To summarize: get a 1:7 [or 1:8 match grade, if not using tracers] twist barrel if you plan on using the military M855 ammo [or Euro SS109] with a 62-grain or heavier bullet. Get a 1:12 M16A1 barrel for M193/ 55-grain or import equivalent, or for use with a .22 conversion. If you have a 1:9 *compromise* barrel and are having good luch with the ammo you're running through it, stick with that load.
And, in general, you want the longest barrel possible, at LEAST a 16 incher, preferably a 20-inch military-length rifle barrel- if you plan on getting both accuracy and bullet expansion on your intended targets.
See the conceited little man’s post at #80. You guys do not have a clue what you are talking about evidently!!!! No ‘serious’ firearms speak here at FR! Why waste your time with us know nothing fellow FReepers...but give ‘im time tho, he is a young’n, he might get squared away someday.
Yeah, no serious professionals here. Gotta go to a “real gun site” to get serious discussions from other keyboard commandos.
I think the collective experience of this board has forgotten more than most other boards can remember.
These “gun guys” are like someone that thinks they are a professional mechanic because they diddle themselves to a Snap-On poster.
To be fair to the many confused people in the firearms hobbies, we have to consider from where they get much of their information: gun rags.
The more I learn about firearms, the less inclined I am to pick up any gun rag, even if it comes to me completely free of charge. The amount of half-truth, obscurantist peddling of stuff that people don’t need, or more accurately, don’t need to BUY, is simply overwhelming in these magazines and periodicals.
The “fashionable” guns of the day seem to attract the most mis-information, if I can be allowed to extrapolate from what I’ve been reading from the last century. For example, it used to be that people hung on Jack O’Connor’s every word as gospel. The .270 130 grain Partition, pushed by 60gr of 4831 powder, was seen by many who hung on O’Connor’s words as entirely sufficient for hunting anything in North America.
I’ve used this exact load on a pronghorn in Nevada and see the Partition fail, coming apart into five pieces. This has reinforced my nagging suspicion that gun writers, as a rule across the decades, are paid to write, and their editors aren’t much concerned with actual, you know, *facts* - so long as the writing helps sell ad space and generate readers. And Jack O’Connor sold a lot of Winchester product in his day, as well as a lot of Nosler’s bullets.
The AR-15 is probably the hottest hobby rifle of this day, as is evidenced by the sheer amount of product aimed at the market space now. We have now the ultimate race for the bottom in the sale of “80% lowers” and so on.
The CO’s bodyguard/driver for near 19 months,,,
He had the best M-4 that could be had,,,
He cussed that M-16 action every time I was able to talk to him,,,
Had to clean it 3-4 times a day,,,
He finally got a shotgun,,,
Back in late ‘67 they tried to give us M-16’s,,,
It took a threat of calling the IG to keep the M-14’s,,,
If you need a rifle to defend you and yours the
AK is the way to go,,,
It will always shoot...
I used to buy the rags, but it’s been at least 10 years now since for the very reason you stated: Product peddling. Nothing told is the truth anymore.