Hey guys I just had a chance to shoot my huldra slank upper (http://www.huldraarms.com/uppers/product_d786a54be56c/) and had quite a few problems with it. I fireed 60 rounds and tried 2 lowers (carbine buffer and a h2 buffer) 3 different mags and kept having the same issue. I had 20-30 rounds that failed to fire, different ammo was used and lowers. Typically those rounds would fire on the 2nd hot but there was 5 or so that needed to be hit a 3rd time. I used federal ae, golden bear and another type. All experienced failure.  No issues loading the next round once it fired, gas settings are regular, suppressed and off, left in the regular position and tried in the off and issue was repeatable in both those settings. Any ideas?

Feel free to email me at [email protected] for troubleshooting or Support.

Cody
Adams Arms
Customer Service Manager

That's a new one. I have the same upper although mated to a Spikes lower. Sounds like you're getting light primer strikes.
Definitely give Cody a call. He and Adams are quite responsive and back up their products.

it looks like a standard firing pin

have you swapped another one in?

Negative all stock upper and standard lowers. Talked to Huldra and they said give the bcg and firing pin a good cleaning and try and give the firing pin channel a cleaning as well, they said there is a preservative grease they use in the channel that maybe slowing the pin down. Talked to Cody already and have that avenue if I need it.

That'd be my guess. I've owned and used several of the "Huldra" variety AA rifles and uppers (including the Slank upper you have) without a problem.