I'm wondering if i messed up in getting a .223 chamber if i intend on using 5.56 ammo? I'm not sure thats what i have as the seller sent the wrong upper but the discription of the one i got says .223 barrel. how can i check the chamber myself?

thanks inadvance. kevin

Most barrels are marked either .223 or 5.56. Does yours have any markings?

5.56 ammo is loaded hotter than .223, and could cause problems in a barrel chambered for .223.

Quoted: Most barrels are marked either .223 or 5.56. Does yours have any markings?

Just (M 1 S  1-9). i took off the handguards and found no markings

NATO 5.56 ammo can increase chamber pressure up to 15,000 psi in .223 SAMMI chambered barrels... That type of increase can lead to a dangerous situation...

ETA:Have you tried to contact M1S to ask them if there is a way to tell what caliber the barrel is chambered in?

Quoted: Have you tried to contact M1S to ask them if there is a way to tell what caliber the barrel is chambered in...

thats a good idea i will try tomorrow, thanks.

Quoted: Quoted: Have you tried to contact M1S to ask them if there is a way to tell what caliber the barrel is chambered in... thats a good idea i will try tomorrow, thanks.

Dont forget to let us know what they say...

Will Do.

I talked to Model 1 Sales today about my upper.  The Guy said mines a .223 and the 5.56's have 5.56 engraved under the handguards on the barrel, noting there if it's a .223. also said he never heard of an incident shooting 5.56 in a .223 chamber.

Quoted: Also said he never heard of an incident shooting 5.56 in a .223 chamber.

From the Ammo Oracle:

Q. What is the difference between 5.56×45mm and .223 Remington ammo?

In the 1950's, the US military adopted the metric system of measurement and uses metric measurements to describe ammo.  However, the US commercial ammo market typically used the English "caliber" measurements when describing ammo.  "Caliber" is a shorthand way of saying "hundredths (or thousandths) of an inch."  For example, a fifty caliber projectile is approximately fifty one-hundredths (.50) of an inch and a 357 caliber projectile is approximately three-hundred and fifty-seven thousandths (.357) of an inch.  Dimensionally, 5.56 and .223 ammo are identical, though military 5.56 ammo is typically loaded to higher pressures and velocities than commercial ammo and may, in guns with extremely tight "match" .223 chambers, be unsafe to fire.

The chambers for .223 and 5.56 weapons are not the same either.  Though the AR15 design provides an extremely strong action, high pressure signs on the brass and primers, extraction failures and cycling problems may be seen when firing hot 5.56 ammo in .223-chambered rifles.  Military M16s and AR15s from Colt, Bushmaster, FN, DPMS, and some others, have the M16-spec chamber and should have no trouble firing hot 5.56 ammunition.

Military M16s have slightly more headspace and have a longer throat area, compared to the SAAMI .223 chamber spec, which was originally designed for bolt-action rifles.  Commercial SAAMI-specification .223 chambers have a much shorter throat or leade and less freebore than the military chamber.  Shooting 5.56 Mil-Spec ammo in a SAAMI-specification chamber can increase pressure dramatically, up to an additional 15,000 psi or more.

The military chamber is often referred to as a "5.56 NATO" chamber, as that is what is usually stamped on military barrels.  Some commercial AR manufacturers use the tighter ".223" (i.e., SAAMI-spec and often labeled ".223" or ".223 Remington") chamber, which provides for increased accuracy but, in self-loading rifles, less cycling reliability, especially with hot-loaded military ammo.  A few AR manufacturers use an in-between chamber spec, such as the Wylde chamber.  Many mis-mark their barrels too, which further complicates things.  You can generally tell what sort of chamber you are dealing with by the markings, if any, on the barrel, but always check with the manufacturer to be sure.

from ammo-oracle.com [Shooting 5.56 Mil-Spec ammo in a SAAMI-specification chamber can increase pressure dramatically, up to an additional 15,000 psi or more.

That just reads like the biggest bunch of hearsay/speculation.  Has anybody pressure tested different chambers with a controled load?  

Quoted: from ammo-oracle.com [Shooting 5.56 Mil-Spec ammo in a SAAMI-specification chamber can increase pressure dramatically, up to an additional 15,000 psi or more. That just reads like the biggest bunch of hearsay/speculation.  Has anybody pressure tested different chambers with a controled load?

Oh come on if someone wrote that with first hand knowlage they wouldn't say "Shooting 5.56 Mil-Spec ammo in a SAAMI-specification chamber can increase pressure dramatically, up to an additional 15,000 psi or more."

Exactly, it can, may not  but it has the potential to.

I disagree, if everything else is equal and you shorten the freebore and tighten the throat angle you will increase pressure, this is a well known phenomenon.  That's not why I would like to talk to someone who has done some pressure testing in various chambers, what I would like to know is to what degree  pressure is increased and what does the pressure curve look like up to PMAX.

I guess I'm going to have to get me one of these, it's on my list after the lathe.

Quoted: I disagree, if everything else is equal and you shorten the freebore and tighten the throat angle you will increase pressure, this is a well known phenomenon.  That's not why I would like to talk to someone who has done some pressure testing in various chambers, what I would like to know is to what degree  pressure is increased and what does the pressure curve look like up to PMAX. I guess I'm going to have to get me one of these, it's on my list after the lathe.

Thats a nice tool for the job... If your a serious reloader or analyst, owning a  chronograph is a must, but purchasing one just to find out the answer to your question?  Hopefully you'll run across someone that has already performed this test and can pass along the answers your looking for so you can save a few bucks...

As we already know, SAAMI specification .223 chambers have a much shorter throat, a smaller diameter bullet seat, and less freebore than the NATO chamber... And that combination does increases pressure... Ive read one place that it could increase up to 10,000 psi and at another up to 15,000 psi... Now that you have me thinking more about it, curiosity has me hooked and I'd like to see the actual differences and wouldn't mind taking a peek at a graph from such a test...

I'm going to look around to see if I can find out any other info pertaining to this subject... If I come across anything I'll pass it along...

This is one of those "old legends" that has been around every since SAAMI and a few other groups (Mostly LE) tested it and released the info a LONG time ago -- SAAMI (whatever they know about ammo) does NOT recommend shooting 5.56 in .223 chambered rifles and specifically list it on there "unsafe combinations" listings. People have tested it (with real pressure barrels) and found an increase of OVER 10,000 CUP...

There are literally hundreds of sites that have this info, this is from gunzone.
Snip...

Almost a quarter of a century ago, SAAMI recognized potential problems with shooters assuming that the 5.56mm cartridge was identical to the commercially available .223 Remington round. Here is their 31 January 1979 release, with some minor errors corrected: With the appearance of full metal jacket military 5.56 ammunition on the commercial Market, it has come to the attention of the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) that the use of military 5.56mm ammunition in sporting rifles chambered for Caliber .223 Remington cartridges can lead to higher-than-normal chamber pressures and possible hazards for the firearm, its user and bystanders. Tests have confirmed that chamber pressures in a sporting rifle may be significantly higher in the same gun when using military 5.56mm ammunition rather than commercially loaded Caliber .223 Remington cartridges, according to SAAMI. SAAMI points out that chambers for military rifles have a different throat configuration than chambers for sporting firearms which, together with the full metal jacket of the military projectile, may account for the higher pressures which result when military ammunition is fired in a sporting chamber. SAAMI recommends that a firearm be fired only with the cartridge for which it is specifically chambered by the manufacturer.

Shoot Smart... Shoot S-Mart

www.saami.org  -->  Publications  -->   UNSAFE ARMS AND AMMUNITION COMBINATIONS

BTW stiles, there is better software, but a "crush" barrel is still probably best, I can get you pressure test barrels if you are interested? And yes, people have tested pressures in the AR barrel in probably every configuration you can imagine... you are not the first to think of it, I have drilled many, many holes all over barrels to take port pressure reading with piezo block clamps and have a great deal of info in computer models, if I can help out at all?

Quoted: I have drilled many, many holes all over barrels to take port pressure reading with piezo block clamps and have a great deal of info in computer models, if I can help out at all?

Gunzilla, maybe you can help me out with the answers to a couple of questions?

Ive been trying to find out what the approximate gas pressure (psi) is that's traveling through the gas tube of a 14.5" barrel while using NATO ammo? Also, whats the minimum psi needed to properly cycle the bolt carrier group?

10,000 CUP man that is up there.  Using the 270 winchester's SAMMI numbers for max pressure (IIRC off hand it's 52,000 CUP and 60,000 PSI) that would make 10,000 cup ~ 11,500 PSI (I know it's not a direct conversion like that but I'm not sure how CUP scales so this may not be valid at all), that's still ~ a 21% increase in pressure if nominal pressure is 55,000 PSI.  If you take the old handloaders general rule that for every 3% increase in velocity there is a 6% increase in pressure you should see a 10.5% increase in velocity which would put a 55g pill that comes out of a military chamber at 3200 fps up to a smoking 3536 fps out of a civi gun.

As much of a bad idea it is to shoot military 5.56 ammo in a civi chamber and the fact that 223/5.56 is on sammi's unsafe combos list (it's actually a funny list, I was looking at earlier tonight, lots of screwed up combos that make you go HUH ) we know it's done daily.  If the nominal pressure increase is 15,000 psi we are in the area of 70,000 psi! Man that's just not going to be extraction and cycling problems over a case of ammo.  11,500 psi would put you at 66,500 psi and I think that much pressure may have made even Rocky Gibbs cringe .

I have some assumptions above about military ammo.  From my understanding it's loaded to velocity and not pressure so I kinda picked 55,000 psi pushing a 55g pill at 3200 fps out of thin air so if I'm off base let me know.

My interest in a system to measure pressure is more towards seeing the pressure curves during load development.  From my understanding the strain gage systems are more appropriate for comparison purposes than nailing down the absolute nuts PMAX.  I don't know anything about the  piezoelectric pressure measuring systems at all other than it's pretty much become the standard in the industry.  If you want to share any insights and thoughts on the various systems I'd be happy to hear from you no doubt.  But there is no rush as is typical with me I have more interest than dollars .