5.56mm NATO versus 223 Remington Chamber Differences

[patrick sweeney]

Colt has only and ever chambered their rifles in 5.56, with the rare exception of some match rifles for special uses. (Don't have my references handy, but as I recall the numbers are vanishingly small.)

If it is a Colt barrel, it is 5.56. The earliest barrels were not marked like today, since there was one chambering (5.56) and one twist (1-12)

Early barrels might have no marking,s or just the letter C stamped where you can see it.

[DCN1]

Great info here but I have a quick question on this subject.
I sometimes see ammo online listed as both 5.56/.223, do we assume these are .223 since the 5.56 doesn't say nato?
Or do we assume the seller just doesn't know any better?

Example
http://www.sportsmansguide.com/net/c...aspx?a=1009676

My rifle is 5.56 so it's not a huge deal either way, just curious.

[patrick sweeney]

Most likely the seller doesn't know, or didn't ask.

Chrono it. If it delivers .223 speeds, it is .223 If faster, it is/maybe 5.56.

Or, if it is cheap (relatively, these days) and for practice/blasting, and you have a 5.56 leade, don't sweat it.

[Iraqgunz]

Prvi Partizan is usually loaded to 5.56 specs and is good to go. They do also make .223 ammo such as the 75gr. match rounds. Some manufacturers often times interchange the two calibers w/o mentioning that the difference is the Mv and some don't even bother to warn about shooting 5.56 in .223 chambers.

Great info here but I have a quick question on this subject.
I sometimes see ammo online listed as both 5.56/.223, do we assume these are .223 since the 5.56 doesn't say nato?
Or do we assume the seller just doesn't know any better?

Example
http://www.sportsmansguide.com/net/c...aspx?a=1009676

My rifle is 5.56 so it's not a huge deal either way, just curious.

[larry starling]

Colt has only and ever chambered their rifles in 5.56, with the rare exception of some match rifles for special uses. (Don't have my references handy, but as I recall the numbers are vanishingly small.)

If it is a Colt barrel, it is 5.56. The earliest barrels were not marked like today, since there was one chambering (5.56) and one twist (1-12)

Early barrels might have no marking,s or just the letter C stamped where you can see it.

Local store has a AR-15A2 Colt marked .223 on receiver. had a fair price on it. But thought it was odd. didn't look at barrel markings btw.

[Iraqgunz]

What's marked on the lower is irrelevant. Even barrel markings are misleading (just look at Bushmaster, etc...with their 5.56 markings).

Local store has a AR-15A2 Colt marked .223 on receiver. had a fair price on it. But thought it was odd. didn't look at barrel markings btw.

[MK75]

That was very informational Molon. Thanks a lot.

[LOBO]

What's marked on the lower is irrelevant. Even barrel markings are misleading (just look at Bushmaster, etc...with their 5.56 markings).

My two Bushmasters have .223/5.56 on the receiver, but they are marked 5.56 NATO on the barrel. I called Bushmaster & they said the rifles could fire both .223/5.56. Is this BS? Should I just stick with .223 ammo? Thanks.

[patrick sweeney]

There is no way of knowing what your chambers are, short of measuring them.

Even the guys at Bushmaster probably don't know for sure. There may be one guy there, who has seen the prints for the barrel, and measured chambers to be sure the supplier is delivering proper product, who knows.

And he isn't saying.

[LOBO]

There is no way of knowing what your chambers are, short of measuring them.

Even the guys at Bushmaster probably don't know for sure. There may be one guy there, who has seen the prints for the barrel, and measured chambers to be sure the supplier is delivering proper product, who knows.

And he isn't saying.

Thanks!