I am troubleshooting my urutau build and having issues with binding in the FCG leading to the hammer getting stuck under the disconnect. Everything is printed in eSun PLA+ and I am using the 3d Print Freedom build kit.

Here is the relevant section of the Urutau documentation in the Dry Firing section 4b: If the hammer successfully released when pulling the trigger, hold the trigger down, pull the charging handle back as far as it will go, release the charging handle, and then release the trigger. When you release the trigger, the trigger should spring forward, and you should hear another audible “click” sound. If no sound is audible, check the inside of the gun to see if the hammer is still attached to the disconnector. If it is, you may need a stronger fire control group housing spring.

The build kit is already using an upgraded FCG housing spring, so I don’t think that is the issue. I have sanded all parts of the lower and FCG where they make contact as well as the surfaces where the hammer and disconnect meet and made sure there are no burs/sharp edges anywhere. Everything is smooth and there are is no debris under the FCG.

What I have found is that it only binds when the hammer is cocked. Everything moves freely until the hammer is ~90% of the way back. Is it possible that the AR hammer spring in the kit too strong? I have loosened and tightened all of the screws multiple times and it doesn’t seem to be an issue with that (also mentioned in the doc as a potential issue)

What can I do for next steps in troubleshooting?