Let me start off by saying I have never built an AR lower which would probably answer my current question if I had but I will remedy that later.  Please see the attached photos below.  I bought the complete lower from Anderson.  I started have feeding problems (bolt failed to chamber first the round) and assumed it was the magazine or upper.  I switched uppers and magazines (both worked on other lowers) and the same problem.  I then began shooting it with the Anderson lower hoping the problem would work itself out.  It did--in a way.After about the 70th round, the barrel nut on the buffer tube broke loose and the spring shot out as shown in the photo.

Is this problem easily fixed by installing a new spring?  I've looked at a lower schematic, and can't determine what the spring is called.  What is it?  Or is this a manufacturing defect in the lower that should be remedied by sending it back to Anderson?  Any information would be greatly appreciated.

There's a little detent on the other end of that spring.

Make sure you don't lose it when you pull the spring out.


You're supposed to stake the castle nut but some blue loc-tite will work too.

Takedown spring and detent. Safety spring is different.

But yes you'll need a castle nut wrench and preferably a spring loaded punch to easily stake the nut

Read this thread for fixing the problem and gaining a greater understanding of your new rifle.  

http://www.ar15.com/forums/t_3_4/226782_Assemble_your_own_LOWER__UPPER__FREE_FLOAT__TRIGGER__GAS_BLOCK___Step_by_step_instructions_.html


Read this thread for a great way to solve the detent spring problem entirely.  

http://www.ar15.com/forums/t_3_118/395777_Simple_fix_for_the_rear_takedown_detent_spring_blues____.html

Do you still have the detent?

Did the receiver extension back out or just the castle nut?

Do you still have the buffer retainer and spring?

I am having a hard time thinking of a reason the lower could cause feeding problems unless it is way out of spec.

You might check to see if the mag release is adjusted properly.

Do you still have the detent? Yes

Did the receiver extension back out or just the castle nut? Just the castle nut.

Do you still have the buffer retainer and spring?  Yes

you're right, got ahead of myself



 

Thank you all for the information!  I will give an update and let you know if I did it properly.

I would buy a spring kit combo from Anderson. It will give you all the detents and springs just in case you need one. Replace the screwed up spring and make sure you did not lose the detent that was behind the spring. If so replace it too. Torque the buffer tube nut and stake it. Staking the buffer nut will stop it from backing out on you again. That's my advice hope it helps

From your picture it looks like the carbine stock adapter plate, which normally covers the take-down pin detent spring, has rotated, which allowed the spring and probably the detent plunger to shoot out of the lower. That happened when the castle nut loosened. You'll have to be careful that the buffer tube is covering the buffer retaining pin properly and then put the parts back in, swing the adapter plate into position and tighten the castle nut, which then should be staked.