Just built a new AR for work. I’m having a FTF issue predominantly on the left rounds of the magazines. 3 different mags tried. Switched my upper to a different lower, same issue. The nose of the round is getting caught up on the top of the feed ramps where the bolt/barrel keys/teeth are. Will chamber after a second charge. Not a gas tube/gas key issue as the FTF is occurring before the gas key engages the gas tube. I’m thinking a feed ramp issue or perhaps the upper is out of spec. Upper and lower are Aero and the barrel is a ballistic advantage 16”. BCG appears to be in good working order. These FTF’s are only happening while hand cycling or letting the bolt release forward after being locked back. I have not had a FTF while firing.

Build has approx 200 rounds through it so far and I know there’s multiple schools of thought on break in etc.

Any advice helps! Will be hitting the range on Saturday to put more rounds through it.

What ammo?

Hornady steel cased 55grn and wolf brass cased 55grn. Both .223. We’ve put the same mags in other rifles and they’ve fed fine.

The current plan for today is to start scratch on the upper. Rebuild with the same parts just to make sure everything is torqued and indexed correctly and put some rounds down on Saturday. The only change to parts would be a new gas tube and gas block, if needed. No indications that it would be the gas tube hitting the gas key either.

We shall see.

It is happening sporadically throughout magazines which leads me to think it may be a feed ramp issue. I’m using pmags, usgi and hexmags. The pmags are by far the most tolerant to the issue and produce less instances of the malfunction. I am trying to figure out how to post pictures. I’ve got them, including what the failure to feed looks like.

I will say that the FTF occurs more frequently on the first 15 rounds than the last 15. It will occur while releasing the bolt via bolt catch and by pulling the charging handle completely to the rear and letting go, but has not presented itself while actually firing. Has me perplexed.

After the mulligan and rebuilding the upper (with help; aka someone else took a stab at it) with all the same parts all seems to be working well. While familiar with the AR platform, this is my first bare bones front to back build. The failure to feed issue has been resolved. Here are a couple of small things that were done that I believe added up to a successful resolution (please note that the real test will be tomorrow when it hits the range again):

-barrel was removed and reseated. 2 less barrel nut shims were used and the barrel nut was increased in torque from 30-50. I attribute this to my unnecessary fear of over torquing and not giving the AR platform enough credit on its durability.

-gas block and gas tube were removed and reseated, checking alignment, pins and set screws.

-buffer spring was replaced with a stronger spring, adding more resistance, allowing more force on the bolt going forward.

-a VERY (read extremely) light polish on the feed ramps to remove any burrs and smooth out any unseen marring.

After the rifle was completely put back together, 3 mags (pmag, hexmag and usgi) were hand cycled through without issue. This was impossible before the corrective action was taken.

The moral of the story: a little bit of inexperience in building from scratch along with some minor discrepancies caused the failure to feed issue. A true example of trial and error on a first time build that was resolved at little cost (buffer spring).

Glad you got it resolved OP. Congrats on that build!

Range was 100% successful. No malfunctions. Got it zeroed and was nailing steel.