Hand cycling a semi auto action will create problems by the dwell time of gravity. I don't think this is the problem, but it happens all the time.
LET THE BOLT SLAM HOME. Do not ride the bolt. The forces involved are identical to the action cycling. The bolt is at the rear most portion of travel when it reverses and moves forward. It's designed to work that way, not hand fed.
You won't get a slam fire unless you are using a really sensitive primer. The AR firing pin does touch it when chambering, it doesn't cause slam fires on military ammo, and no known research shows that sensitive civilian primers are any better at improving anything in the AR. Very few seem to be that touchy, anyway. Getting them flush when seating is far more important.
M4 feed ramp cuts were designed by Colt to improve reliability in full auto fire - the ancient cheap magazine design will let one rattle loose in combat and having the cuts improves reliability feeding it. There's million's of M16's without them, they have a softer cyclic action and don't pop rounds out of the magazine as much. It's a carbine length action thing (big hint about HD and SHTF use - go to mid length.)
This is a common situation in new AR's - hand cycling the action is kinda like testing to see if the clutch will withstand a full power dump at the dragstrip by doing it at idle. Not the same thing at all, sure it stalls. In this case, filling up with regular (factory ammo) and going to the strip (range) is needed first. Then science out the special fuel when the platform is known to be good to go.