am i an idiot?

[mr40.cal]

pardon my ignorance but isnt a 5.56 NATO the same exact bullet as a 223 rem? maybe thats why my gun has had so many malfunctions? i know it says on my bushy barrel that its chambered for the 5.56 nato, but for some reson i always thought that it was the same as the 223. am i crazy?

[Circuits]

Yes and no. Their external dimensions are identical, but their loading data and chamber specs are different.

The real difference is in the chamber dimensions, but even most barrel and rifle manufacturer's aren't strict in their observation of marking, since they are used interchangeably by many, if not most people.

Military firearms intended to use 5.56mm NATO rounds have a longer "leade" which is the portion of the barrel in the throat before the rifling starts, and have a longer allowable headspace than .223 Remington SAAMI spec. Each military firearm has its own chamber specification - so M249 SAW has a different specification and set of gauges than the M16/M4. They're longer and looser than .223 Rem spec, to accomodate sustained full auto fire with enhanced feeding and extraction reliability.

Back to ammo, mil-spec 5.56 NATO ammunition uses thicker brass (hence less internal volume), and gets loaded to pressures up to 10% higher than allowable for .223 Rem SAAMI spec. The thicker brass keeps the round together in the looser chamber of the military firearm, but in a tight sporting chamber, it's like compressing the load, and can spike pressure levels higher still.

That said, a modern .223 in good condition can usually safely fire 5.56 NATO spec ammo - it's about like firing hot handloads, but an older or worn firearm might break under the additional strain, especially from repeated and regular use.

A 5.56 NATO chambered rifle can safely fire .223, but the loads will generally seem weak, and the commercial brass will probably stretch a bit more than the thicker military brass, leading to fewer safe reloading cycles, and possibly some pressure signs or case ruptures on used brass in a well-used NATO chamber.

[damion]

I think someone else had answered that question already on this forum. Circuits is correct though.

[USMC NAM GRUNT]

My Bussy won't cycle 5.56 NATO worth a damn but I've never had a bit of trouble with .223 Rem. :D

[mr40.cal]

Thats interesting:rolleyes: