Cross Machine Tool makes a big-bore AR slick side upper: https://www.cmttac.com/AR-15-Receivers/ ... pper-upur3
Currently out of stock with them, but they're making more soon.
Meanwhile, Ranier Arms has them in stock now: https://www.rainierarms.com/cmt-tact-up ... ust-cover/
Also: https://www.nokick.com/CMT_UPUR_3_AR_15 ... upur-3.htm
And a side charger: https://www.rainierarms.com/cmt-tact-up ... e-charger/