I've been away from the Armalite platform for a while, so I'm trying to get current on what fits the original AR-10. My rifle is an Armalite AR-10T built about 10yrs ago with all components coming from the Armalite company. At the time, I was well aware of the differences between Armalite and the AR 308 differences. Fast forward a decade and I'd like to add another upper to my rifle with a different barrel profile. I know Armalite was sold (again) so I'm a bit lost even after visiting the Armalite website. I see they have both A & B series but haven't pinned down a definition just yet. Since I see Eagle Arms also on the site, I'm guessing this might designate the two different platforms??  If anyone can provide some insight, it would certainly be appreciated. Thanks!

You have the "B" model if it's 10 years old. Steel magazines are all B models

Thanks for clearing things up, I appreciate it!