Armalite AR10 in 243

[Tann]

I have an Armalite AR-10 that was sold to me as chambered in 243, but the markings on the lower receiver display 7.62mm. 243 chambers perfectly into the gun but 7.62x51 does not. Is this a 243 gun?

[98Z5V]

On 1/23/2024 at 6:54 AM, Tann said:

I have an Armalite AR-10 that was sold to me as chambered in 243, but the markings on the lower receiver display 7.62mm. 243 chambers perfectly into the gun but 7.62x51 does not. Is this a 243 gun?

Have you shot .243 Win through it?

The lower receivers are usually stamped for the main cartridge that the rifle was built for.  Age of the lower plays a big part here, with more modern lowers simply marked "Multi," for multi-caliber.  The main concern for you is what is the stamping on the barrel(?)...  That determines the caliber for the (these) large-frame ARs. 

Irregardless of what's stamped or engraved into the lower receiver, the primary focus is what the barrel markings state.