5.56 NATO in a 223 Boltie

[rbernie]

I know that the 5.56 NATO round is cut a little fuller (sorta the Docker's version of 223), and the conventional wisdom says that it's OK to run 223 in a 5.56 chamber but not vice versa.

But if the 5.56 round will chamber OK in a 223 rifle - why would it be bad juju to run it?

 

[ckyllo]

5.56 has alot more chamber pressure than .223 and the gun may not be strong enough to handle the round ( KABOOM )! may not ever happen gun may run fine on it but it isnt something any ammo or gun company is going to be ok with. have also heard of unfired rounds getting stuck trying to get them out

 

[kaferhaus]

I've never heard of a .223 rem bolt gun being damaged from firing a non defective NATO spec 5.56 round. NATO ammo is usually a bit "hotter' than the civilian counterpart but they are by no means "over pressure" rounds.

A modern bolt action rifle is MUCH stronger than any service rifle autoloader around.

The biggest difference between .223 and 5.56 is the 5.56 chamber has considerably more "free bore" than the civilian chamber, this is for functional reasons only.

I've shot thousands of rounds of NATO spec ammo in various bolt guns for practice/plinking and never had any signs of pressure, no flat primers, hard extraction, bulged bases etc. never a one.

 

[ckyllo]

some reading on the subject:

http://www.ammo-oracle.com/body.htm#diff

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

http://www.saami.org/unsafe3.htm

 

[rbernie]

NATO ammo is usually a bit "hotter' than the civilian counterpart but they are by no means "over pressure" rounds.

Actually, in my searches for this answer last night, I came across this from SAAMI: "The .223 Remington is rated for a maximum of 50,000 CUP while the 5.56mm is rated for 60,000 CUP."

Now, I don't think that an additional 10000cup will blow up a modern boltie, but it's gotta be A Bad Thing for it.

 

[Art Eatman]

I fail to see how an M16 action is stronger than a bolt-action.

I go along with kaferhaus. I shot a bunch of "surplus" 5.56 "liberated" from Fort Hood, through my first Mini-14. Never noticed any ill effects at all.

I guess the military crimp around the primer pocket is the main safeguard against this 60,000 psi figure. After all, the big problem for most handloaders who get into overpressure range is the blowing out of primers. Most rifles (or the designs) are proof-tested to around 90,000 psi; some, above that.

Art

 

[rbernie]

I've been debating getting a 223/5.56 rifle for a while for both small game use and to have something that can use 5.56 NATO if that's the only thing that's locally available. I really don't need the cost/features of an AR, so I've been conteplating getting a Vanguard chambered in .223 and taking my chances with the occasional use of MilSurp ammo.

I fail to see how an M16 action is stronger than a bolt-action.

It suspect that it's not. I also suspect that the AR chamber has less meat around it than most commercial bolties, as well...

While I'd never advocate making a diet of over-pressure rounds in a rifle, I suppose that its safe to suggest that having a .223 eating 5.56 is better than having a 303R and having only 5.56 around....

 

[Coltdriver]

rbernie,

I don't know what you mean by "cut a little fuller". Externally they are dimensioinally identical.

The differences in the two rounds are that the military version has a crimped primer, a little more internal web at the base of the case, and a crimp at the neck.

The idea is that 5.56 has a rougher life in a full auto m-16 than standard .223 and these features are there to beef up the ammo to prevent changes in length from being banged around in the magazine.

The combination of extra webbing (less area for the same amount of powder) can theoretically lead to higher pressure if you reload to .223 formulas.

The crimp in the neck is one thing I can think of that would cause a higher pressure. The other is that if you have a really tight SAMMI spec or target (even tighter) spec chamber in your .223 then you run the risk of getting the bullet too close to the lands. That can dramatically increase pressure. It is never a bad idea to know the actual dimensions of your particular chamber as they do vary from model to model.

When you reload .223 you are usually filling the case up and then compressing the powder with the bullet. As long as you are staying with powders in the recommended range this is a non issue for a healthy rifle.

I have never heard of a healthy rifle blowing up from any 5.56 or .223 round and although the warning may be valid with an older rifle the .223 round came out in the 60's (I think) so there are not going to be antiques chambered for it anyway.

 

[rbernie]

As far as I can tell from the following, the 5.56 chamber throat is a Docker's version of the .223:

http://home.sprynet.com/~frfrog2/miscelld.htm#5.56 mm NATO

 

[kaferhaus]

The 5.56 has a longer freebore (throat)

This is the same system that Weatherby used to keep from blowing up rifles chambered for his magnums.... the bullets get a pretty good jump before they ever contact the lands which reduces the pressure "spike". However the military didn't do it for pressure reasons, they did it for reliability reasons.

The previous post that mentions the up to 10,000 psi increase in pressure when a 5.56 is fired in a 223 is a "worst case" senario. You'd have to be shooting a tight chambered short throated chamber to approach that number.

Ever check your freebore in your commercial chamber for reloading?? Chances are you've got well over .100" freebore if your ammo is loaded to SAAMI maximum OAL! Bolt guns that I handload for usually end up with the ogive of the bullet just kissing the lands... this gives me the best accuracy in most rifles, BUT you have to work those loads up..

This senario is extremely unlikely from just usuing NATO spec ammo in your bolt gun.. and even the worst case senario, 60,000 psi aint gonna blow up your gun or even damage it...

SAAMI minimum proof pressures for 223 is 90,000 PSI which is still a 50% margin...

 

[BigG]

5.56 also has to work with belt feed mechanisms, much rougher usage than a sporting cartridge. Thats why everything on the .mil ctg has to be screwed together so tight.

 

[kaferhaus]

5.56 also has to work with belt feed mechanisms, much rougher usage than a sporting cartridge. Thats why everything on the .mil ctg has to be screwed together so tight.

This is obviously very true and an excellent point. Military ammo has to be assembled to sustain treatment that sporting ammo would never face.

When you think about it, it's amazing that this stuff is as accurate as it is.