Many ARs do not have a built in fixed front sight. If there is a rail, fold down back up sights can easily be mounted. (Magpul has good backup sights.) They are normally folded down and only used as a backup. Scope mounts usually are tall enough to look over the front sight. if fixed. Co-witnessing is usually done with red dots without magnification.

4 acre pond 32 ft deep within East Texas (Livingston) timber ranch. Filled (to the top of an almost finished dam) by Hurricane Harvey 9/17. Stocked with FHM, CNBG, RES 10/17. Added 35lbs RSC 3/18. 400 N LMB fingerlings 6/18