Axel, the Sharps bros Showdown lower is multi caliber Wich means it can be used for any AR-15 caliber you wish to build. So 223/5.56, 300 blackout, 7.62×39, 6.5 Grendel, 224 Valkyrie, all the way up to 50 beowulf. I just built an AR15 in 224 Valkyrie wich is a great caliber, pretty much 223 on steroids. The Sharps bros Showdown lower will work great with any caliber you want. As for building an AR at first it seems difficult but promise you it's actually pretty simple. Just Google anything you don't Know and watch plenty of videos and you'll be fine. Hope this helps and good luck.

Axel, the Sharps Bros Showdown Multi-Caliber Lower will run any standard AR platform calibers like 5.56/.223, 300BLK, 6.5 Grendel, 6.8SPC, .50 Beowulf, .458 SOCOM, 7.62x39mm etc. The bolt is key. Some info here : gunsamerica.com/digest/build-an-ar-15-ar-calibers/#:~:text=Build%20an%20AR-15%3A%20AR%20Calibers%201%20.223%20Remington,SOCOM%20...%208%20.50%20Beowulf%20...%20More%20items