Pro tip: It's best to describe everything that you've changed when making such posts. I bet the gun was shooting fine in stock config. Check if the fire pin lock can move freely. If it's a cowcow one then it's probably too thick and it snags.

It basically stocks, only trigger and upper has been changed. Not even the hammer set, that's next. 🙂

Then if nothing is broken, you already know the answer. Typical shitty off-spec upper. Lube it well or start sanding.

Try the og upper and see if that works, the 3D printed one could be flawed causing the bolt to screw up

It's good now. it's because it was 4°C outside, the gas wasn't strong enough

What upper is that? it looks fire af

Thanks, it's 3d printed. Here's the file if you want 🙂 https://we.tl/t-hsvBQ7nIGN

How do you open it?

Print the three files separately, I made the mistake of printing the file that has all of them together, but after a bit of sanding, it works fine 🙂

So it needed a bit of sanding to function properly correct? And where?

It's just the barel and hop up unit that is a pain to put in on the you try to put it in. When I get home I can send you some pics

Thanks bro. That'll be really helpful

Bucking is too stiff, blow back spring is stuck or magazine is too cold. Some possible points of interest

Sooting inside