.223 vs. 5.56mm

dustyhol

I have a stupid question. I recently purchased a RRA M4 rifle and it is marked 5.56mm on the gun. When I look at the RRA website it says ".223/5.56 NATO chamber". My question is what round to shoot/reload for this gun? I have a .223 rifle and the dies to reload for this caliber. Is this the same or do I need to buy/reload different dies, brass, etc. Thanks! I don't want to make a mistake with this type of stuff!

sandwarrior

dustyhol,

The outside dimensions are the same. The difference between .223 and 5.56mm Nato is more a matter of pressure limitations. If your rifle shows .223/5.56mm, it will probably shoot both without damage to the rifle. The biggest factor is that a rifle designed for military use fires a restrictive range of bullets. The powder used is chosen for it's ability to produce the maximum amount of pressure behind the bullet yet be completely burned enough so that it won't overpressure the gas recovery port, or overheat it. This is under the given criteria of sustained fire, rapid fire, etc. Most civilian rifles will fire NATO ammo without any problems. The same is not always true of military rifles. Some .223 loads use longer burning powder and are higher pressure made for bolt action rifles. For the above mentioned reasons stick to milspec ammo for military rifles or at least a relatively close load to military. -good luck

Edit:
I should clarify that a 'restrictive range' means bullet weights and velocities within a given range, i.e.e 55 gr bullets pushed out at 3250 and 62 gr. bullets pushed out at 3100 fps. Like mentioned there is a lot of variance in the manufacture. BUT, military rifles aren't designed to take everything from 40gr. all the way up to 90 gr. Only match military rifles should be shooting 68 gr. and heavier. And while the sides of military chambers are a little roomier the headspace is not. That is a sure way to have a big problem in any rifle...long headspace. I fire military ammo in my bolt action all the time and don't have any problems with headspace. And that is because the outside dimensions of .223 and 5.56 Nato are the same. When milspec ammo goes in my rifle it headspaces on the shoulder.

Gunslinger2005

The guys at AR15.com has a site called the Ammo Oracle that has a wealth of info on ammo. Check it out: http://www.ammo-oracle.com/body.htm

Hawk Carse

Military calibers tend toward roomy chambers for use in hot dirty combat conditions with wide tolerance ammunition made by wartime contractors and "allies." In particular, the 5.56 has a chamber throat cut for clearance in case it gets some ammo with a funky nose contor, and there is a little relief in the shoulder area in case the odd looking tracer bullet gets deformed when fired. Chamber headspace runs long, too.

I don't know what Rock River means by calling their chambers both at once. Tolerance ranges overlap and they may have chamber dimensions at the high end of commercial - low end of military specifications.

Your .223 Remington dies will work fine. Keep an eye on your fired brass for signs of casehead separation in the bigger GI chamber and adjust the sizing die to not set back the shoulder any more than necessary for easy chambering. If you have to make a change on that, I would say to keep separate brass for each gun so as to not have casehead separation or difficulty chambering.

All the warnings you read are based on really extreme end of tolerance range mismatch and are not very likely with good quality barrels and ammunition.

temblor

The dimensions are slightly different on 5.56 vs 223 rem. -- mostly in the throat or leade area of the chambers. The 5.56 has a longer throat and some military ammo will sometimes show high pressure in the commercial 233 Remington chambers. This is not usually an issue when the commercial ammo is shot in the military chamber.
As Sandwarrior noted some types of powder are not the best suited to the gas operated guns though.
Most problems usually surface when trying to shoot military ammo designed for automatic or semi-automatic guns with the longer chamber in commercial 223 rem. bolt action guns that lock up tight and don't use any of the gas pressure to operate the action.
There are wide variances in 5.56 ammo depending on what country/factory that it was made in. NATO ammo is manufactured all over the world and quality control varies greatly.
Unless you are going to shoot NATO ammo in a commercial bolt action chambered rifle, most likely you will never see a problem.
You can load/shoot 223 ammo in the 5.56 marked guns, but you should try to use a powder that is the proper burn rate in the semi autos.
Good Luck.........[8D]

nononsense

dustyhol,

You do not need separate dies for the different chambers although the suggestion of keeping the brass separate is a great idea and is the usual practice.

Here is the list of common chambers and the differences between them:

http://www.radomski.us/njhp/cart_tech.htm

There is actually a series of chambers that get used in rifles depending on the application for those rifles. The variables are the throat angle, leade length (freebore), and maximum OAL with the SMK bullets. In this illustration, note that the SAAMI chamber is set to accommodate varmint length bullets as opposed to the longer target length bullets used in competition.



RRA seemingly has used one of the hybrid chambers that allow for the use of most if not all cartridge lengths. It has been referred to as the .223 Wylde chamber. You might give them a call to see what their explanation is.

Best.

dustyhol

Thanks for all the information guys. I'll keep my brass separated and watch for any problems.