The AR series in BRM5 include the M4A1, MK18, C7A2, M16A2, M16A4, M110 and HK416A5. All of these guns excluding the M110 and HK416A5 are being revamped in the next update.
They have similar firing systems and interchangeable parts but not the same and ar15 isn’t the family. It’s a member of the auto loading rifle family the guns you listed are apart of the full automatic auto loading fsmily