.223 Ammo vs. 5.56mm ?

[Bob96]

  I remember reading once that military 5.56 ammo should not be used in Contenders chambered in .223. Is there a difference in case dimentions or headspace?  I know that the military adopted the 5.56 from the available .223 but don't know if they made changes in the dimemtions or pressure rating?  Can these be interchanged today in a T/C.?

[swampthing]

It depends on the manufacturer of the ammo. "Military" brass tends to be thicker, which allows for less powder, compared to "standard" .223 brass. For a given powder charge, pressures will be higher in the "military" loaded round, all things else being equal. I don't think we're talking about 8-10,000psi here, but they tend to be a little hotter.

[skarke]

Very important question!!!!  IT IS NOT SAFE to shoot 5.56 military ball ammo in a .223 barrel.  I know lots of people do it, but it is wrong.  While the military ammo is designed to conform to higher pressure standars, that isn't the only problem.

Many TC barrels have tight chambers, and particularly, minimum throats.  If you cram the longer 5.56 cartridge into a shorter .223 throat, you might pinch the end of the casing into the sides of the bullet, GREATLY increasing pressure.  This is complicated further by the 5.56 military ball being designed for 60000 cup.

JMHO, but I kind of like my eyesight.

[Steve P]

5.56 Nato is "military" and has to be made to specific "mil specs".  .223 is made per SAAMI specs.  Mil specs and SAAMI specs are not the same.  5.56 Nato will fire in a dirty firearm.  They also have crimped in bullets and crimped in primers to seal them. 

I am a member of a LARGE shooting club.  Many of the guys shoot the military matches with old military mausers, garands, etc.  They also shoot M15s, M16s, ARs, etc.  One month they will be shooting groups with military or surplus ammo.  Next month or big matches they will be shooting their reloads with commercial brass. 

The main thing here is to know your gun and know your ammo.  I won't beg, buy, or borrow someone elses reloads to shoot in one of my guns.  I also will not shoot ammo I am unfamiliar with in my guns. 

My .223s have seen lots of Remington, UMC, Winchester, WCC, PMC, and Federal ammo.  I also have hundreds of reloads using this same brass.  This is mixed military and commercial with no problems.  None of my guns have ever seen steel cased ammo.  I know nothing about it.  I am also very picky with military surplus from outside the country, unless it was made by, or for, the country where the gun was manufactured or used.  I have several military rifles and use the original military ammo made for them.  With these, the concern comes with the commercial.  I have to read up on it before I can use it.

Know your gun.  Know your ammo.  Shoot safe.

Steve