I have "Cal .223-5.56mm" written on the side of my DPMS Panther.  Is it true this means both 223-5.56 can be used?  I know the differences in casing thickness and primer between the two, but didn't know there was a rifle configuration that could safely shoot both with no longer term negative effects.  So is this "smart" marketing by DPMS to misleadingly convince buyers I can shoot 556 in a 223, is it a 556 that can safely shoot 223, or something else?

Thanks

What is marked on your barrel? Is it marked 5.56 Nato? If so the answer is yes you can shoot both.

From Wikipedia:

5.56 mm NATO versus .223 Remington[edit source]

The 5.56 mm NATO and .223 Remington cartridges and chamberings are similar but not identical.[36] While the cartridges are identical other than powder load, the chamber leade, i.e. the area where the rifling begins, is cut to a sharper angle on some .223 commercial chambers. Because of this, a cartridge loaded to generate 5.56mm pressures in a 5.56mm chamber may develop pressures that exceed SAAMI limits when fired from a short-leade .223 Remington chamber.

Brass casing[edit source]

The dimensional specifications of 5.56 NATO and .223 commercial brass casings are identical. The cases tend to have similar case capacity when measured, with variations chiefly due to brand, not 5.56 vs .223 designation. The result of this is that there is no such thing as "5.56 brass" or ".223 brass", the differences in the cartridges lie in pressure ratings and in chamber leade length, not in the shape or thickness of the brass.[37][38]

Pressure[edit source]

C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56 mm NATO, at 430 MPa (62,366 psi). This differs from the SAAMI maximum pressure specification for .223 Remington of 380 MPa (55,114 psi), due to CIP test protocols measuring pressure using a drilled case, rather than an intact case with a conformal piston, along with other differences.[39] NATO uses CIP pressure test protocols for their small arms ammunition specifications.

Because of these differences in methodology, the CIP pressure of 430 MPa (62,366 psi) is the same as a SAAMI pressure of 380 MPa (55,114 psi), which is reflected in US Military specifications for 5.56 mm NATO, which call for a mean maximum pressure of 55,000 PSI (when measured using a protocol similar to SAAMI).[40]

These pressures are generated and measured using a chamber cut to 5.56  NATO specifications, including the longer leade. Firing 5.56mm NATO from a chamber with a shorter .223 Remington leade can generate pressures in excess of SAAMI maximums.

Chamber[edit source]

The 5.56 mm NATO chambering, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Rock River Arms)[41] or the ArmaLite chamber, which are designed to handle both 5.56×45mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also differ from the 5.56 mm NATO chamber specification.

Using commercial .223 Remington cartridges in a 5.56 mm NATO chambered rifle should work reliably, but until recently, it was believed this was less accurate than when fired from a .223 Remington chambered gun due to the longer leade.[42] Although that may have been true in the early 1960s when the two rounds were developed, recent testing has shown that with today's ammunition, rifles chambered in 5.56mm can also fire .223 ammunition every bit as accurately as rifles chambered in .223 Remington, and the 5.56mm chamber has the additional advantage of being able to safely fire both calibers.[43] Using 5.56 mm NATO mil-spec cartridges (such as the M855) in a .223 Remington chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and SAAMI recommends against the practice.[44][45] Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56 mm NATO, such as many commercial AR-15 variants and the Ruger Mini-14 (marked ".223 cal"), but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56 mm NATO ammunition.[46]

It should also be noted that the upper receiver (to which the barrel with its chamber are attached) and the lower receiver are entirely separate parts in AR-15 style rifles. If the lower receiver has either .223 or 5.56 stamped on it, it does not guarantee the upper assembly is rated for the same caliber, because the upper and the lower receiver in the same rifle can, and frequently do, come from different manufacturers – particularly with rifles sold to civilians or second-hand rifles.

In more practical terms, as of 2010 most AR-15 parts suppliers engineer their complete upper assemblies (not to be confused with stripped uppers where the barrel is not included) to support both calibers in order to satisfy market demand and prevent any potential problems.

Good point about lower vs. upper, but both are from the original sale from DPMS.  I can't find the manual, and there are no other markings than on the lower as I said: "Cal .223 - 5.56 mm".

Thanks for the article, but I already know the difference in calibers - I need to know, preferably from someone familiar with DPMS products, if that is accurate and it is (basically) chambered for 5.56 so both are OK, or if this was them lying (which I've heard of happening) and it's actually just .223.

This is important, because I'm about to buy bulk 5.56 which I've never shot through it.

What's marked on the lower is essentially irrelevant. Go by whatever is on the barrel

If you want to shoot 5.56 you need to see what the barrel is chambered for. Your lower is fine to shoot either. What is stamped on your barrel?

Have to remove quad rails, one sec.

Edit to follow.


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It's not on the barrel anywhere... any other suggestions besides calling the manufacturer with my serial number?  The lower and upper both came from DPMS as one unit, if it says what I said it says twice now, what does that mean?  Is it safe to assume the manufacturer was saying it's 5.56 and can work with .223, or is that reasonable doubt?

The stamping should be visible in front of  the front sight base. Look for something that reads like 1/9 5.56 NATO

Edit: Look between the front sight and flash hider on top of barrel

Should look like this.

http://img209.imageshack.us/img209/8636/hpim3132co2.jpg

Thanks, but unfortunately nothing is written on my barrel - nothing at all.  Just smooth black from the base up to the front sights.

I LIED!  That picture helped, thanks - I didn't look BEYOND the front sight post.  It says 5.56 1 -9, so I'm good for both, thank you!

While I'm here asking questions, what does the 1 -9 mean?

It is the barrel twist rate it means the bullet makes 1 turn every 9 inches. Different twist rates for heavier/ lighter bullets

Thats the twist rate of your bbl. Means the the bullet will turn once per 9". Basically you can shoot all ammo up to 69gr (but sometimes exceptions can occur). Have fun with your new stick.


 

please read all the tacked threads as well as the owners manual, you really need it. make sure you read the ammo oracle, it covers all these basic questions





 

of all the sources on the net you quote wiki???





you couldn't have used something like oh lets say something from here http://www.ar15.com/ammo/?




 
 

Read the threads at the top of each section that answer all of the most common questions that people tend to ask without looking to see if it has been discussed before. These so called "sticky threads" are in most every section and the amount of information in them is priceless. Good luck with your new rifle!

Great information. I was also wondering  same thing about my newly/ first AR-15.

DPMS sells many rifles that shoot 5.56.

Their lower marking "strategy" -- as you say -- is NO different from any other mfg.


The markings on the lower are irrelevant.  However, if this is a factory gun that you purchased brand new, the lower should be accurate.


But that's NEVER what you use to check.  You MUST check the barrel markings.  My guess is it's going to read, "DPMS, 1:9, 5.56"



You're working real hard to demonize DPMS.  But it is your clear inexperience with the entire AR platform that is causing you to effectively humiliate yourself.  Any hobbyist with experience who has tinkered with AR's knows that the caliber markings on the lower receiver mean nothing.  Many companies mark "multi" on their lowers.  "Is this a safe marketing strategy?  They're telling people they can put 105mm Howitzer rounds in there."

No.  Read the barrel like everyone else.  DPMS sells many AR's that shoot 5.56; the AP4 being one of them.





ETA:  Now that I read your other posts, it is confirmed you aren't familiar with the platform.  There are many "tacked" threads in this forum area that will help you with the other questions you have asked, as they are basic questions.  I promise you that 99% of your questions have already been asked and can easily be found.  Simply Googling your question and adding the phrase "ar15.com" to your entry, will yield links to threads in this forum that will answer your questions.  Good luck on your reading, and enjoy your new rifle.