AR15 caliber headache

[Pinard]

Man O man, same question over and over online. Read this. I can send you a picture of both 5.56 and .223 chambers that have been bisected to illustrate a bit better.
With a .223 chamber vs 5.56 chamber, the amount of "freebore" that a .223 chamber has before the rifling begins is about HALF of what a 5.56 chamber has. This alone is enough to cause spikes in pressure by shooting the hotter 5.56 ammo in a true .223 chambering.
BUT IF THAT IS NOT ENOUGH TO DETER YOU, The ANGLE of the rifling in a .223 chamber is almost vertical while the angle of the 5.56 is much more tapered and gradual. Think of it as the bullet meeting a "cliff" with the steep rifling angle in a .223 chamber.
BUT more of a "ramp" with the gradual rifling of a 5.56 chamber.
You may have lucked out with getting a 5.56 chambered gun that was stamped .223rem to slide by some export rules, but the only way to be sure is to have a chamber cast made which will also show the leade and rifling angle. Go to your gunsmith and get it done. It's cheap and no guesswork needed anymore.

Got my answer this morning from OberlandArms directly:

Hi,

just purchased an OA 15 and see it's marked for .223 caliber. Is it still safe to fire 5.56x45mm ammo through it?

Thank you

sure, no problem.

--
Mit freundlichen Grüssen / best regards

Matthias Hainich
Oberland Arms ohg
Am Hundert 3
82386 Huglfing

 

[P of PDent]

I have an older OA-15 from when The Shooting Edge brought them in and it is similarly marked as Kal 223 Rem. however it has a DPMS HB upper (got it in a trade years ago). Fantastic accuracy, match trigger with a machined billet lower. Phil.

 

[Sqr]

I shoot 5.56 in my .223 , mostly the Norc stuff , it shouldn't be a problem as long as the ammo is loaded to spec , it you have flattened primers or gas streaks on the primer , then the ammo is bad and shouldn't be used .

And for those of you who are a little preachy about how the rifle will go super nova on you if you use 5.56 in a .223 , Show me where you've seen this , because , aside from bad 5.56 ammo that would of blown up any rifle in 5.56 , I've never seen 5.56 ammo destroy a .223 rifle .

Its fear mongering as it will never cause an issue in a new .223 chambered rifle. Also as stated some countries will not allow the sale or even the use of Military use ammunition to avoid said countries civilian ban.

The difference between .223 and 5.56 is similar to the differences from one .223 manufacturer to another or one 5.56 manufacturer to another.