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Old March 1, 2002, 07:52 PM   #1
Ray HP
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.223 vs 5.56 chamber dimentions

.223 vs 5.56 chamber/brass dimentions

I could not find any threads on this subject using the search function. Joe Portale mentioned in the 223 sticking bullets thread that he had previously posted a thread on this subject. Any help will be appreciated.

Thanks
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Old March 1, 2002, 08:52 PM   #2
Bill Adair
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Ray,

Not sure I can help, as I have only one .223, an Encore 15" pistol.

What I can tell you, is that the Winchester white box .223 that was on sale at Midway last month, would not chamber in my Encore! The bullets touch the rifling before the case spaces on the shoulder. Incidentally, this ammo advertised as .223, is actually marked 5.56mm, not .223.

I measure the free bore on my Encore by dropping a new bullet into the chamber, and measuring the depth from the breech face to the bullet base, and determined that max OAL was a bit shorter than the manuals call for. I reloaded some of the Federal cases accordingly to 2.21", and they work just fine.

I also ran a box of the Winchester rounds through my seating die at that same setting, and that cured the problem.

Federal Classic 50gr Hi-Shok marked .223 REM, chambers fine, right out of the box.

I've never seen exact measurements to verify, but have heard that military 5.56 chambers are looser (what ever the heck that means) than commercial .223 chambers.

Bill
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Old March 1, 2002, 10:32 PM   #3
Art Eatman
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The shape of the bullet is more likely to cause a problem than any case dimension variance.

Years ago, there was a fair amount of GI ammo which was "liberated" from Fort Hood and found its way to Austin. It worked fine in Mini 14s and in Colt AR 15s.

In recent years I've bought gunshow reloads with GI brass; shoots just fine in a Ruger 77 or in a Bushmaster.

The case dimension deal is the wall thickness of GI brass. For the .223, the .308 and the '06 it's thicker than civilian stuff.

If the leade is fairly short in a particular rifle, it's fairly easy for a slow-taper ogive to hang up in the rifling.

Art
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Old March 2, 2002, 02:06 AM   #4
Bill Adair
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Art,

That's correct, I think bullet shape has everything to do with proper seating depth.

My RCBS seater die contacts the ogive at one particular point between the case mouth and tip, but all bullets do not have the exact same shape, so what's right for one bullet may be wrong for another.

Where the seater die contacts the bullet, has no relation to where the rifling contacts the bullet, unless the lands in the rifling, and the ID and taper of the seater stem contact point are identical. This is almost impossible to standardize, with all the variations in bullet shape, and barrel ID.

Dropping a bullet into the chamber, and measuring to the breech face also has it's hazards, as individual bullets from the same box seem to have some variations in slope or length. Thus one bullet will give a different measurement than another from the same box.

I found very early on that OAL is almost a meaningless number, unless measuring for fit in a particular magazine, because seating on the ogive produces variations in OAL, due to the variations in ogive slope.

Bill
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Old August 22, 2002, 05:28 PM   #5
MeekAndMild
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Revisiting this thread, I have learned from The Gun Zone .223 vs 5.56 FAQ that there is indeed a difference in the Leade before the rifling starts.

Now, my question is how do you tell the Leade of a rifle. Do you chamber a cartridge and look for rifling marks on the bullet? Is there a special gauge? Can you look in and see?
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Old August 22, 2002, 06:19 PM   #6
Bill Adair
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M&M,

There are several chamber measuring devices on the market, but some of them are quite expensive, but I wonder if they really do the job properly.

A product that might help is Cerrosafe, a chamber casting material available from Brownelle's, for as little as $12 for a half pound.

It melts at low temperature (below the boiling point, so is safe to use in any rifle), and can make a casting of your exact chamber dimensions. The product can be re-melted as often as you like, and comes with detailed instructions.

Bill
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Old August 23, 2002, 05:14 PM   #7
MeekAndMild
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Thanks, Bill.

I'll look it up.

Another thing I thought of was to load a couple of primerless cartridges with lead bullets varying amounts over maximum length and see if I can get a mark on them when chambering them.

1 hour later, edited post. I just ordered some. It's 12 bucks for 8 ounces and reusable. A lot cheaper than an exploded barrel. I figure with this heat the 5.56 may be significantly over the 60,000 max listed pressures.
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Last edited by MeekAndMild; August 23, 2002 at 07:09 PM.
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Old August 25, 2002, 05:38 PM   #8
Bill Adair
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M&M,

Good, Let me know how it goes with the Cerrosafe casting. I alway wanted to try some, but never got around to ordering any.

My Encore chamber was too tight for the Winchester .223 white box ammo recently on sale at Midway, so I resized an empty case that had been fired in my gun, and seated a bullet without crimping. Left the bullet about as far forward in the neck as I could, without it falling out. Chambering that round gave me a starting point for chamber length, by shoving the bullet back into the case when it hit the rifling.

I then adjusted my seating die till it just touched the bullet, and tightened it down a few thousandths at a time until the round would chamber without touching the rifling at all. Tightened down another ten or twenty thousandths from there, and that's what I use for seating depth.

OAL of a loaded round is practically meaningless except to determine magazine fit, and the ogive shape of bullets is what actually touches the seating stem in a good die, and not the tip of the bullet.

I figure with this heat the 5.56 may be significantly over the 60,000 max listed pressures.

What heat? I live in Seattle.

Bill
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Old August 25, 2002, 08:59 PM   #9
Bud Helms
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Bill Adair: "I found very early on that OAL is almost a meaningless number, unless measuring for fit in a particular magazine, because seating on the ogive produces variations in OAL, due to the variations in ogive slope."

Hear, hear! Good on you, Bill! Especially, when OAL is given to 3 decimal places!
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Old August 25, 2002, 11:23 PM   #10
Bill Adair
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Sensop,

Thanks.

When I first started rifle reloading, I thought at first there was something drastically wrong with my methods, because I could not get a consistent OAL with my .223 reloads?

No matter how carefully I trimmed cases, adjusted dies, and seated the bullets, there were relatively large variations in OAL! Certainly nothing close to the precision OAL measurements published in most reloading manuals!

Puzzled, I measured the length of a dozen or so bullets from a couple of new boxes I had on hand, and found that it varies all over the place, for any given bullet! Then I realized that most of the reloading manuals have it wrong!

Minimum cartridge length is obviously very important, because it effects case pressure, as is maximum cartridge length for proper feeding in magazines and some rifle actions, but stating OAL to three decimal places is both confusing and misleading.

Bill
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Old August 26, 2002, 07:32 PM   #11
MeekAndMild
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Quote:
Chambering that round gave me a starting point for chamber length, by shoving the bullet back into the case when it hit the rifling.
Did it leave a mark on the bullet? I was reading that some folks use a long lead bullet for the same effect.

I'll wait on the Cerrosafe's arrival and let you know in a few weeks how it turns out. Stuff is SUPPOSED to shrink for the first half hour after its poured.
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Old August 26, 2002, 11:52 PM   #12
Bill Adair
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M&M,

Don't remember for sure, but I think the rifling did leave tiny nicks in the bullet jackets?

Cerrosafe will not help you determine OAL for your reloads. It is great for checking chamber condition, and proper dimensions, but I don't think is was intended to be use for OAL measurements.

I'd still be interested in hearing what you find.

I would not use anything but the actual bullets you are reloading to determine OAL. Even changing to a different bullet weight, from the same manufacturer and type, may effect OAL, because the slope (ogive) of the bullet can vary.

Bill
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Old August 27, 2002, 09:27 PM   #13
Buford Boone
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Try this link:

http://www.winchester.com/law/news/news.eye?storyid=11
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Old October 2, 2002, 10:11 PM   #14
MeekAndMild
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Bill, the Cerrosafe works. It is reusable but one needs a little funnel to pour it right.

The Sinclair Chamber length gauge works in bolt action rifles and costs $4.45 per size. It is put into a sized but uncrimped cartridge then carefully chambered.
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Old October 7, 2002, 07:49 PM   #15
Bill Adair
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Buford,

Thanks for the link. Interesting information, and it spells out the differences between 223 and 5.56 chambers exactly.


Meek,

Glad the Cerrosafe worked for you.

Last weekend, I found it offered at a gun show by folks I usually buy bullets from, so now I know where to get it locally when needed.

Bill
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