Identification of 5.56 on barrel.

[13081]

I have a A2 that I acquired used in a trade and the lower states 5.56/.223 but I do not know that the barrel matches for a fact.
Before I load this with 5.56 is there a SIMPLE way to identify this?
I am not interested in testing with 5.56 to find out as this seems to be a bad idea.
I can not find any numbered indication on the barrel.
Also, I do not have any tools precise enough to measure the bore.

Does this need to go to a gunsmith to verify?
Thanks in advance.[Beer]

[Circuits]

The only way to know for certain without making a chamber cast is if the manufacturer is known, has unambiguous markings, and is known for sticking with their making and marking procedures. That's going to limit you to modern Bushmaster, most Colt and non-match-marked Armalite barrels. Also, government spares contract barrels should all be properly marked, and will have 5.56 chambers.

Other makers have mixed and matched over the years, and either didn't mark, or inconsistently mark their barrels, so without a chamber cast, there's no way of being 100% sure.

Even a gunsmith may have trouble telling the difference, if they don't know what to look for. Chamber dimensions are the same between .223 SAAMI and 5.56 M16 military spec, the only differences are in the throat for leade and freebore. There's an oracle and FAQ over at ar15.com in their reference section that goes over the chamber difference in great detail. Here's a link to Winchester's views on the issue http://www.winchester.com/lawenforcement/news/newsview.aspx?storyid=11

[DOC]

There isn't any markings on the barrel? They usually are on the barrel near the front sight block.