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IronMaiden67
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Posted: 5/31/2009 12:04:22 AM
I got my upper at the gun show today. It's a RRA A4 with 18" bull barrel with a 1:8 twist. They list it as a "wylde" chamber, so my question is what is the exact definition of a .223 "wylde" chamber?
MZMan
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Posted: 5/31/2009 12:13:56 AM
I have the same chamber on my 24" bull upper.

Its basically made to shoot both .223 and 5.56 but I do not know what physically makes it different. There must be something that deals with the differing pressure.
iNeXile556
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Posted: 5/31/2009 1:00:29 AM
CLICK

(save me typing time )
I find it ironic that the product that protects my couch when I spill my drink is actually named "Scotch Guard".
IronMaiden67
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Posted: 5/31/2009 9:26:36 AM
Thanks guys! now I have learnings on this I'm going out to the range to break it in today. I was kind of sceptical about the extra wieght in such a short rifle, but this "wylde" chambering may make up for that in the long run.
Joe_Sakic
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Posted: 5/31/2009 11:47:01 AM
Originally Posted By IronMaiden67:
I got my upper at the gun show today. It's a RRA A4 with 18" bull barrel with a 1:8 twist. They list it as a "wylde" chamber, so my question is what is the exact definition of a .223 "wylde" chamber?


IronMaiden67,

Here's a good article by Glen Zediker:

Chambers: that all-important point where everything starts

So I don't leave anything out, I'm going to start this off pretending nobody knows nothin'. A rifle chamber is a hole cut in the breech end of a barrel so a round of ammunition will fit. It's a lathe operation. A "chamber reamer" is the tool that cuts this hole and it is shaped the same as a cartridge case with at least part of a bullet stuck in it. The reamer is going to cut out the case body and shoulder silhouette, the case neck, and then extend into the bore to form a bullet profile silhouette. It's here, the bullet profile area, where major tooling differences exist. There are a lot of different .223 Remington reainers. The two most commonly used in factory-done guns are at opposite ends of this universe––one is the shortest, and one is the longest.

Let's look closer. What I called the "bullet profile area" is technically called a "leade." We can also call it the "throat." Inside the chamber, the distance between the end of the case neck and the first point cut into the rifled portion of the barrel coinciding with the barrel's land (rifling) diameter is the preeminent variable determined by the reamer. Land diameter will be the smallest dimension inside a bore. If the first point of full land diameter (usually 0.219" in a 224-caliber barrel) is farther from the end of the case neck (farther into the bore), then the chamber has a longer leade or throat. The bullet won't contact the lands until, of course, it reaches the point on the bullet that coincides with land diameter. I call this the first point of "major diameter" on a bullet. The effect or influence of this conical space ahead of the case neck is simple: The more space the less pressure, and the more space, the farther the bullet must "jump" until the bullet contacts the lands. Read all that again.

Mole Hill And Mountain

Now, SAAMI (Small Arms and Ammunition Manufacturer's Institute) long ago set its standards for .223 Remington based on bolt-action rifles chambered for this round. These bolt rifles were configured for varminting. There was, of course, originally a military chamber and round in use since the .223 Remington commercial round was renamed from the 5.56x45mm (NATO-spec) cartridge. The SAAMI chamber has a good deal shorter leade or throat than a military NATO-spec chamber. There is material elsewhere addressing the reasons this was a bad idea (SAAMI's bad idea), and it's become an even worse idea because it's never really been adequately explained to the folks––like you and me––who load or purchase ammunition for AR-15s. See, off-the-shelf AR-15s can have either chamber. Even worse, some barrels are not marked and some are improperly marked. Compounding matters (but not necessarily making them worse) is competitive use of AR-15s resulted in even more chambering options, and reamers. These came about when 80-grain bullets became available and immediately popular. The SAAMI chamber was too short and the NATO was too long.

So the rest of this will make sense, the following dimensions are all based on an overall cartridge length that will have a Sierra 80-grain MatchKing bullet just touching the lands when the round is chambered. We don't all shoot Sierra 80-grain MatchKings, and we don't all set them to touch the lands, but most competitive High Power Rifle shooters do both. At the least it's a "standard" that gives us a point to work from. What I call the "Derrick Chamber" (Derrick Martin of Accuracy Speaks) needs an overall cartridge length of 2.442"; the "Wylde Chamber" (for competition-use AR-15 pioneer Bill Wylde) is 2.445"; the "AMU Chamber" (for U.S. Army competition team) is 2.500". There are others, but these are the most popular among competition rifle builders. A SAAMI chamber is normally about 2.410"; a NATO chamber is normally about 2.550". Those are huge differences, and I counted five different reamers just mentioned here.

So the rest of this will make sense, the following dimensions are all based on an overall cartridge length that will have a Sierra 80-grain MatchKing bullet just touching the lands when the round is chambered. We don't all shoot Sierra 80-grain MatchKings, and we don't all set them to touch the lands, but most competitive High Power Rifle shooters do both. At the least it's a "standard" that gives us a point to work from. What I call the "Derrick Chamber" (Derrick Martin of Accuracy Speaks) needs an overall cartridge length of 2.442"; the "Wylde Chamber" (for competition-use AR-15 pioneer Bill Wylde) is 2.445"; the "AMU Chamber" (for U.S. Army competition team) is 2.500". There are others, but these are the most popular among competition rifle builders. A SAAMI chamber is normally about 2.410"; a NATO chamber is normally about 2.550". Those are huge differences, and I counted five different reamers just mentioned here.

Bad? Worse? Better?

Which generally bad thing is worse, or better? Chambering specification doesn't matter all that much to accuracy, but it can to round performance––not the same thing. The .223 Remington has a short case neck, a small body and, well, it's not the perfect round for 600-yard performance. It is, however, what we have to work with. Making it work its best means giving as much room as reasonably possible to the long bullets. This is done to prevent seating them so far back into the case. We need all the powder capacity we can get. I'm a fan of longer rather than shorter leade specs. Others disagree. There's no answer that can't be argued beyond an average man's concept of a "day."

The good news is a longer throat doesn't seem to matter to the performance of shorter bullets. That's not to say it couldn't matter, but for it to positively influence groups using, say, a 77-grain Sierra MatchKing, the throat would have to be way shorter than what anyone uses in a High Power chamber. I've jumped to my own conclusion that once bullet-jump exceeds a few thousandths I'm not sure it matters. Jumping .015" isn't going to help much more than jumping .035". Reality is that we're shooting targets for score, and, therefore, we must judge the supposed good or bad effects from compromises by score. It's really common and easy to clean a 300-yard High Power Rifle target, with a high X-count, in a "long" chamber shooting "short" bullets, like the Sierra 77. That target has a 7" 10-ring.

5.56MM NATO VS. SAAMI .223 REMINGTON

Pay attention to this! Out of the box, chances are an AR-15 will have either a SAAMI or a NATO chamber. There are huge differences. Specifically, 5.56x45mm NATO specs call for a longer leade than SAAMI defined for commercial .223 Remington (which was originally determined for bolt-action rifles). Leade is the portion of the barrel ahead of the chamber where the rifling has been conically removed to allow room for the seated bullet. A shorter leade raises pressures. Compounding this, military ammunition is nearly always loaded to higher pressures than commercial. Shooting 5.56mm mil-spec ammo in a SAAMI "minimum" .223 Remington chamber can jump up chamber pressure 15,000 psi, or more. Not all AR-15 barrels are correctly marked, and some aren't marked at all. Know by asking the manufacturer, or just shoot ".223 Remington" ammunition and don't worry. Know also before selecting loading data. If loads were worked up in a NATO chamber (Colt HBAR, for instance), they will be overpressure if used in a SAAMI chamber.

NOT TOO TIGHT

Don't get too "precise" in chambering an AR-15. Leave that to the single-shot crowd who tediously and continuously prepare their ammunition. Don't ask for a headspace that's too tight (short), a neck diameter that's too small, a body area that's too close to new case dimensions, or a leade that's too short. The limits, to me, are found in looking at the ammunition you want to be able to fire in the rifle, and also what you want to obligate yourself to in the way of making dimensional corrections in your handloading process. I believe that an AR-15 chamber should be able to accommodate just about any ammunition. The good news is that you won't see any difference in on-target performance. This rifle can't show it. The main effect of "matching" ammo specs and chamber specs is longer case life and less dimensional change firing to firing. Have the chamber polished and keep it clean!

Cheers!

Sakic #19