Bushy chamber question

[Maniac]

A friend has a preban Bushmaster XM15-E2S with a 20" H-bar. The lower receiver is marked "Cal. 223-5.56MM". Does this mean the chamber is a Wylde or merely that the rifle will handle both rounds equally? It will shoot sub .5 MOA with premium ammo. The barrel itself is marked "B MP 5.56 NATO 1/9 H BAR"

TIA

Information

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[corben1]

The barrel tells the story, not the lower. Appears to be a 5.56 NATO.

[Maniac]

The barrel tells the story, not the lower. Appears to be a 5.56 NATO.

That's what I was thinking but it shoots great groups with premium commercial 55gr. ammo, thought that was unusual for a true 5.56 barrel.
Thanks

[corben1]

Don't believe all you hear or read. Form your opinions with experience.