Thomas - It is nothing more than a cosmetic difference. Many manufacturers have gone to the "multi" designation to help avoid this confusion. Both rifles have the exact same style lower receivers. NO reason for any concern, as there are no mechanical or dimensional differences whatsoever.

It is because a receiver is not caliber specific you can change the uppers on either of them and shoot a different caliber like .223, 5.56x45mm, 6.8 SPC, 5.45x39mm, and FN's 5.7x28 or "Five-Seven. some companies change the markings on their receivers because of this and some companies chose not to mark a caliber on a receive at all

Thomas, Adams Arms and other manufacturers have started "Stamping" Lowers as " Multi-Cal" to better inform the public that they can be used for calibers other than 5.56/223 such as .300 Blackout, 6.5 Grendel, 6.8 SPC, .458 SOCOM, .50 Beowulf etc.

It is because a receiver is not caliber specific you can change the uppers on either of them and shoot a different caliber like .223, 5.56x45mm, 6.8 SPC, 5.45x39mm, and FN's 5.7x28 or "Five-Seven. some companies change the markings on their receivers because of this and some companies chose not to mark a caliber on a receive at all

It is 5.56 NATO and 223 caliber so listed as multi caliber