AR 15 Chamber

[survivalshop]

Interesting article 

RELOADERS CORNER: AR15 CHAMBER OPTIONS

JANUARY 19, 2017 GLEN ZEDIKER LEAVE A COMMENT

It’s vital to understand “which” chamber is in your AR15. What you don’t know can create big problems. Here’s why.

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Glen Zediker

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I’ve talked over or at least touched upon this topic, here and there, in other articles. And this week I got four phone calls asking for advice on “which” AR15 chamber I’d recommend. I guess that sort of spurred creation of this article. My primary goal (always) is to answer questions, and ideally before they are asked. So…

A TRUE NATO load always has this mark on its base: the cross-in-a-circle stamp. Some commercial ammo that appears to be mil-spec may or may not be, but err on the safe side.

There are a few options today, and, no, it never was “simple.” There have always been two distinct chambers cut for .223 Remington and 5.56x45mm NATO. And that’s the difference right there! See, .223 Rem. is a commercial round, 5.56 is a mil-spec round. Yes. They are “the same,” but they’re not. The difference is in how these two are loaded with respect to pressures. NATO is a whopping lot hotter. To the tune of +15,000 PSI.

The differences in the chambers are, pretty much, that a NATO has a significantly longer throat or leade or freebore, whichever term is preferred. This is the area in a chamber that extends beyond the case neck cut.

I use a Hornady LNL OAL gage to find out exactly the length of the chamber throat. Get one at Midsouth. This read shows “NATO” by the way. Sierra 80gr MatchKing at 2.550 inches to touch the lands. Wylde should read 2.475. SAAMI-minimum will (usually) be 2.395.

This area in a chamber accepts the initial gas expansion, so, in one way, it can be looked at like an expansion chamber. More room for expanding gases effectively reduces stress on the case. When this area is lengthened, there’s more room, less pressure build. When this area is shortened, there’s less room, more pressure build.

As said, .223 Rem. is short, NATO is long. Take a NATO-spec round and fire it in a .223 Rem. chamber and there’s too much pressure. The .223 Rem. will “fit” just fine; there’s no influential differences otherwise in chambering specifications between .223 Rem. and 5.56.

You’ve probably heard all that before. It’s very important to know. “Which” chamber affects making loaded ammo choices, and also in interpreting reloading data.

Here’s “real” NATO fired in a commercial .223 Rem. chamber. Ouch. The imprints and general beating the case head shows are the result of the additional pressure in the NATO loading, and the .223 Rem. chamber’s inability to excuse that much extra pressure.

Short history as to the reasons these two chambers exist: .223 Rem. in civilian, commercial application was a varminting-type round, along the lines of .222 Rem. When SAAMI (Sporting Ammunition and Arms Manufacurers Institute) laid down the specifications for that round it did so based around the prevalent short .224 bullets of the day, which were often 52-grain flatbase designs. For best accuracy with the little bullets, the throat was kept short, decreasing the distance the bullet had to travel to engage the lands or rifling. Some, most, me included, call this chamber a “SAMMI-minimum.” The mil-spec ammo assembled for M16s used a 55-grain boat-tail loaded to a higher velocity, and the longer throat was specified to handle the extra gas.

What matters is knowing that you don’t have a .223 Rem. chamber. A NATO can handle anything.

Most AR15s I’ve handled in the past good long while have NATO chambers. It’s the only thing that makes any sense for someone, anyone, who wants to fire sto-bot ammo. Not all the mil-type commercial loads (like the “white box” varieties) are true NATO spec, but if the ammo is not marked “.223 Rem.” it might be a tad amount to a lot hotter than a short-throated gun should handle. True NATO ammo has a distinct marking on the case base.

There is now another what’s become “standard” chamber for AR15s, and that’s the Wylde. Named for AR15 accuracy pioneer Bill Wylde, this reamer specs fall between SAAMI-minimum and NATO. Bill started cutting these chambers for NRA High Power Rifle contestants who needed more room in the throat to accept the long 80-grain bullets but not so much room that the shorter 69-grain bullets were having to leap a gorge to engage the lands. A compromise. A Wylde is a good chamber, and a good choice.

Here’s the best way to see what’s going on with AR15 chambers. These are Sierra 80-grain MatchKing bullets loaded to an overall cartridge length that has the bullet touching the rifling. Left to right: SAMMI-minimum .223 Rem.; Wylde; NATO. Wahoo. Big, big differences. There’s a little more than 0.150 inches between the SAAMI-minimum and the NATO and that space in the throat handles the extra PSI of NATO-spec loadings. It is also, by the way, how to know (or one way to know) the actual “length” of a chamber throat.

Here’s how it breaks down, according to me:
SAAMI-minimum or commercial .223 Rem. chamber is good for those who are wanting the best accuracy from light bullets. Can’t run mil-surplus ammo or NATO-spec commercial though.

NATO is for anyone who wants to shoot anything and everything out there safely.

There’s a few ways I’ve seen “NATO” marked on barrels, and I’ve seen a good number of barrels that aren’t marked at all. That’s terribly irresponsible. Look for “5.56” since that seems to have become the more common way to denote “NATO.”

Wylde is more or less an “Improved NATO,” and my experience has been that it will safely handle true NATO loads, even if that’s not its intended design. I base that on spent case condition. It will shoot a little better than a NATO with lighter, shorter bullets. The Wylde is available more and more commonly now from different manufacturers and in “drop-in” accessory barrels.

If you have a “.223 Rem.” stamp on your barrel don’t feed it any ammo that is not clearly likewise marked “.223 Rem.” Should say the same on the case headstamp. If it doesn’t read “.223 Rem.” do not fire it in a barrel stamped “.223 Rem.” This ammo is safe for any AR15. If you don’t see a stamp on your barrel, find out…or just fire .223 Rem.

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The preceding was adapted from Glen’s newest book, Top-Grade Ammo, available here at Midsouth. For more information on this book, and others, plus articles and information for download, visit ZedikerPublishing.com

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[sketch]

Thanks ss!

[survivalshop]

     The issue I have with this article , is with the Bullet comparison between the three Chambers , why an 80 gr. SMK , just how many load this Bullet or use factory ammo with it loaded ? Now this is a good comparison for Match shooters , but i would have liked him to use a 55 or 62 gr. Bullet for comparison & then not only show the results as he did with the 80 gr. SMK , but also the difference between the Bullet touching the Lands & what the bullet is seated in the factory ammo .

  I think one see's that , it would change the narrative of this article  .

 One other thing that irritates me about these writers , they give the pressure spec's , but don't say that the difference in pressure is the MAX pressure per Sammi spec's of the Cartridges , they are definitely not loaded to those spec's , so why use them in a comparison as if they are used . No doubt the two .223/5.56 have different MAX pressure spec's as per SAMMI spec's , but no manufacturer loads ammo to MAX SAMMI spec's , no one !

  They also don't tell you the .223 case is not as strongly made as the 5.56 case to handle the extra MAX pressure .

   So , why use that as a comparison , they are being overly safe , because they are liable for the articles they are writing & should be . I can tell you , that blow ups from ammunition are probably caused by hand loaders or using incorrect caliber ammo in a Chamber .

   I'm not telling you to go out & shoot 5.56 in .223 , but I can tell you from experience , that I have shot thousands of 5.56 in .223 chambers with out an issue & vice versa & o issues , I guess I should of had blown up rifles laying around . 

Edited January 25, 2017 by survivalshop

[jtallen83]

I wondered why he didn't use the 77 grain SMK for a comparison, lots of factory ammo out there with that bullet.

[98Z5V]

I've never seen an 80gr factory load that will fit in an AR magazine...