re: AR15 having issues

Gas tube alignment

Strip down your bolt carrier group to just the carrier and see if it slides freely into the gas tube like in that guy’s video.

Feed ramps aren’t perfectly aligned but it might not even be your problem. I would check the gas tube alignment first. If that doesn’t work I’d try a different bolt carrier group.

Put one round in and see if it ejects around the 3 o’clock or 4 o’clock position. If the BCG and gas tube are aligned and it isn’t ejecting, your buffer spring or weight may be too stiff or you may not be getting enough gas (check your gas block alignment and port set screw). Once you get it cycling that way, still use one round at a time but this time insert a mag. Each cycle should lock the bolt back. If that works, then move on to multiple rounds in the mag at which point you’ll know if you need to realign or carefully file and smooth the ramps.

Or bring the whole gun to an armorer and be done.