Most aftermarket AR-15 barrels to have a 5.56 chamber, also known as NATO. This is the MIL standard and should not be confused with a .223 Remington chamber.
Now, .223 Remington, which is technically SAAMI-spec commercial ammo, and 5.56 NATO (mil-spec) ammo are patently the same dimensionally—either will chamber in either chamber.
The difference is the ammo pressure level. NATO is radically higher pressure.
So, even though this warning has gone around and around for years, here it is one more time: Never fire NATO-spec ammo in a .223 Rem. chamber.
My routine recommendation is to go with a NATO chamber in your new barrel. That means any ammo is reliably chambered and safely fired.
Over the past several years, another option is increasingly available, and increasingly popular, and that is a Wylde chamber.
It’s also greatly misunderstood Or at least based on what I read around the forums.
Bill Wylde (I call him Yoda) was one of the early pioneers in pushing the boundaries in AR-15 accuracy. When the AR-15 was (finally) approved for use in NRA High Power Rifle competition, Bill set out to exploit the accuracy potential of this platform.
Much of that potential could not be realized until there were better .224-caliber bullets available.
Back then (around 1990), the best was the Sierra 69-grain MatchKing, which required nothing special beyond a faster-twist-rate barrel (1:9).
With the introduction of the 70-, 75-, and 80-grain VLD designs and shortly after, the Sierra 80-grain MatchKing, that world changed. It wasn’t long until the AR-15 became the Service Rifle champion, toppling the M14 from its former place of prominence.
NRA High Power rules require firing rounds fed from a magazine for the rapid-fire events. For the slow-fire events, including the all-important 600-yard stage, rules say the rounds must be loaded one at a time.
And those new extra-long bullets had to be seated out a good deal beyond magazine-box length limit.
Important: When I make reference to shorter and longer in a chamber, I’m talking about the space ahead of the case neck, the area that leads in to the rifling, also known as the leade or freebore.
It’s kind of a funnel. This is the difference in a .223 Rem. chamber and a NATO: The NATO has a considerably longer leade, which provides more volume for expanding propellant gases to occupy (lower pressure results).
Also, another term: jump. That is the gap the bullet has to pass through to engage the lands. Generally, the less the better (when the bullet is floating in space, it can lose alignment with the bore).
That commercial-spec .223 Rem. chamber was too short.
This chamber (often now called a match chamber or SAAMI-minimum) meant these longer bullets had to be seated well back into the case, even when seating depth was adjusted to let the bullet touch the lands at rest in the chamber, and that ate up valuable volume that otherwise could be occupied by propellant.
Bill Wylde thought the NATO was too long. So the chamber he blueprinted a reamer to produce was right in the middle.
The Wylde chamber is a compromise, not an ideal. Bill’s idea was to improve performance with the long bullets by giving more freebore and also at the same time to hold jump to a shorter gap with the shorter 69-grain (and later 75- and 77-grain) bullets loaded into magazine-fed rounds.
There were others from other pioneers, such as Derrick Martin, that leaned a little closer (shorter) to commercial spec, but the Wylde chamber became the most popular, and that’s because, overall, it produced the best scores.
If you look at the reamer specs for SAAMI-commercial, NATO, and Wylde, you’ll see that the Wylde is indeed right in the middle in throat length.
The way NRA High Power shooters talked about chambers was based on the overall cartridge length that would put a Sierra 80-grain MatchKing touching the lands. So, given that—and these numbers are indelibly in my head—a SAAMI was 2.395 inches, Wylde 2.475, NATO 2.550.
That, in fact, is what a Wylde chamber is and its entire and complete point and purpose for being.
Should you get one? Maybe. Compared with a NATO, a Wylde offers a shorter jump to the lands with any bullet. That’s a bonus.
In my experience in firing a whopping lot of rounds in competition through NATO chambers, and even also through one longer than a NATO (a custom reamer for 90-grain VLDs), once jump gets over 0.015 or so, there’s not much improvement.
What really matters to accuracy for a jumping bullet is the leade angle, and the shallower the better.
Wylde and NATO use 1.25-degree and 1.20-degree transition angles, which are very shallow (and one way to get the longer chamber). That’s a more gentle transition for the bullet compared with the SAAMI-spec 3.2-degree leade.
The rumor is that a Wylde is fully capable of handling the pressure of genuine NATO-spec ammo. That, by my experience, is true, but define “handle.” A NATO chamber still provides lower pressure, and that is measurable by inspecting fired cases.
If you’re looking for a shorter barrel (16 inches or less) and that’s also coupled with a shorter gas system ( carbine port location or less), I’d stick with NATO.
I sincerely doubt you’ll see a measurable improvement in group size, but you will see an increase in pressure. Again, that doesn’t mean a Wylde won’t be safe, it just means exactly and only what I said: still a little lower pressure with NATO.
I think the best application of a Wylde is for someone looking to maximize ammo performance, which combines accuracy with velocity, in a rifle-length setup. And this is especially true for the handloader who wants the option of choosing and using the longer bullets.
Understand, though, that moving a long bullet out to touch the lands in a NATO chamber results in excellent accuracy and still more propellant space. The difference is in magazine-length-round performance, and that’s the edge the Wylde gives us.
If you are never going to fire NATO-spec ammo and never want to experiment with the longer, heavier bullets, best accuracy with SAAMI-spec .223 Rem. commercial rounds still may come from a SAAMI-spec .223 Rem. chamber, and that’s because it offers the shortest jump. Or not.
Again, the leade angle has a lot to do with that.
Do you know the difference between a .223 Remington chamber and a Wylde chamber? What camber does your AR-15 have? Share your answers in the comment section.
The preceding is based on material in Glen’s books Top-Grade Ammo and America’s Gun: The Practical AR-15. Visit https://www.buyzedikerbooks.com or http://www.zediker.com for more information plus downloads from Zediker Publishing.