Running a A5 system on a 14.5" Adams Upper. Standard weight BCG.
I'm encountering multiple FTFs. I get a clean 4 o'clock ejection, but 90% of the time the bolt is going home with nothing in the chamber.

Here are the different things I've tried.

- Checked piston rod and cup to ensure it was straight and true. Examined piston spring, buffer spring, and BCG for any binding. All appears to be in order.

- Gas system full on > Gas system on suppressed (no can)
*Suppressed lead to FTEs, w/the bolt face locked back 1/4" from the ejector port which I would consider normal function unless I had a can on the muzzle.

- Multiple 30 Rd PMag > 20 Rd Thermold
*Never get more than one shot from a PMag.  2-3 sporadically from the Thermies. Did not have any STANAG mags on hand to test.

- 10 oz Heavy Buffer > 4.6 oz H1 Light Buffer
*No change

- XM193 > XM855 > Fusion 62 gr
*No change

Edit:
- Checked to ensure Rifle, and not a Carbine length spring was used.


Unlike AA's aftermarket kits, their fully built upper comes with a staked gas block so I wasn't able to examine if the ports were possibly misaligned, but that's extremely rare on a staked block that was factory tested (I presume) before being shipped.

I'm left thinking that perhaps the A5 is a contributing element to the  problem since it's the only other 'non standard' operational component on the rifle.

I left the rifle with a well known gunsmith in another state to see if he can  possibly work out what's going on. Of course being good often means being in demand, and being in demand is commensurate with a 4-5 week wait time so I won't be seeing that rig until Decemeber (maybe).  

Still, for my own education and edification I'll like to see what others think.

FWIW, I've run an A5 H2 buffer for 1500 rounds on my 5.45 carbine AA upper with no issues.  I had three FTF but they were caused by light primer strikes with a GI type trigger group.  An SD-C made those go away.  Whose spring are you running and how many rounds on it?  I'm using a Springco Green rifle spring.  I think the next logical step is to check function on another lower.

Come to think of it, silly question, but you didn't get a carbine spring mixed up in there did you?

Using a Wolff XP Rifle length spring. Unsure of the round count but I know it's over 250.

That did cross my mind as I ran through a mental punch list; I  was worried a carbine length spring might have gotten mixed up so I pulled it out and measured it to confirm.

Lower is a Spikes ST-15.  Rarely a problem there but I can't rule it out either until it has been tested.