I just got a brand new lower from PSA to go with my 20" PSA upper. I am performing a functions check. While holding the trigger down. I pull the charging handle back and let go. However the bolt carrier group stalls mid cycle, and does not move forward into battery until I let go of the trigger. Any thoughts?
Did you add any oil to the BCG?
Yes. I applied lube where the bcg makes contact with the hammer as it cycles.
What about the area the of the BCG that make contact with the upper receiver?
Do you have a mag installed? Are you riding the charging handle (i.e. holding onto it)?
Function check should be as follows:
SAFE
Pull the charging handle to the rear and release. Place the selector on SAFE. Pull the trigger, and the hammer should not fall.
SEMI
Place the selector on SEMI. Pull the trigger and hold to the rear. The hammer should fall. Continue to hold the trigger to the rear, pull the charging handle to the rear, and release it, Release the trigger with a slow, smooth motion until the trigger is fully forward. The hammer should not fall. Pull the trigger. The hammer should fall.
No mag in magwell. Yes I am performing the functions check correctly. Its when I hold the trigger to the rear and pull the charging handle back and then let go. The BCG stalls mid cycle. It has also done this while shooting live rounds. Is this just the break in period?
Where are you seeing wear patterns? On the BCG or upper, mostly. Or the hammer, maybe. That should indicate what is binding. There are lots of possibilities of what it could be. If you don’t hold the trigger when cycling, does it work correctly? Do the upper and lower function with different lowers and uppers, if you have any to try?
Going to need pictures
Will send pictures soon. There are signs of friction on the hammer and the bottom side of the BCG. But I thought thats normal.
Wear on the bottom of the BCG is normal. The BCG pushes the hammer down when cycling and this contact can wear both surfaces slightly. It’s not a lot of pressure though, so the wear should only be cosmetic. That’s the purpose of the tiny black spring in between the bottom trigger bar and the disconnector when firing. It gives it a bit of room to depress the hammer. You can test this movement pretty easily, though not exactly the disconnector spring. With the hammer back, finger off the trigger, you should still have the ability to press the hammer down slightly with spring pressure. Roughly 1/4" of vertical movement. Below are pictures of hammer up, and me pressing it down slightly. This is a PSA mil-spec trigger which looks the same as the EPT trigger, if you have that instead. You didn’t say you if had any sort of upgraded trigger beyond this type.
Wonder if the hammer isnt catching as it cycles…check and make sure the disconnector isnt frozen or the spring missing.
That was my first thought. Is the disconnector holding the hammer until you release the trigger and then does the hammer catch on the sear?
If you have another AR , test new lower with other upper and vice versa.