AR lower issue, help needed.

[haus]

I have a CCMG mil spec lower with a dpms parts kit, a knock off mil spec stock tube. My upper is a Noveske 16" in 300 blackout. On the 4th shot the bolt came back and did not load a round. Pulled back to load and it jammed. Finally got the upper and lower apart and the top of the buffer retainer was damaged and the buffer retainer had come out of its hole along with the spring. Buffer retainer obviously has to be replaced now, should I also replace my tube? Do you think its out of spec and not far enough over the buffer retainer to hold it in place when it cycles? This is my first attempt at building an AR and these were my first few shots ever with this gun.

It was bad ass quiet during the shots I did get to enjoy!

[jppd47]

Did the castle nut come loose? That can cause the buffer tube to back out some and the retainer pin to come out and jam up the bolt. Ask me how I know . Did you stake your castle nut?

[Libertarian_Geek]

.the buffer retainer had come out of its hole...

Like the previous post mentioned. The tube is the only thing that captures the buffer retainer (on your particular lower), so your root cause is going to be around the area where the tube comes in contact with the retainer.

Recap. Sorry, I don't feel like doing a full-blown Ishikawa/fishbone diagram, so this'll have to do:

The bolt jammed to the rear. Caused by:
1>The buffer retainer is out of its hole and restricted the bolt's movement from going forward. Caused by:
1.1>The buffer retainer wasn't captured properly. Caused by one of the following:
1.1.1>the tube wasn't forward enough to capture the buffer retainer. Caused by the following:
1.1.1.1>Original installation position wasn't screwed into the lower far enough.
1.1.1.2>The Tube un-screwed at some point. Contributing Factors are:
1.1.1.2.1>The castle-nut was loose. Contributing Factors:
1.1.1.2.2>The castle-nut wasn't tight enough on original installation.
1.1.1.2.2.1>The castle-nut had no additional retention methods. Contributing Factors:
1.1.1.2.2.1.1>The castle-nut wasn't staked.
1.1.1.2.2.1.2>The threadlocker wasn't used on the castle-nut.
1.1.1.2.2.1.3>The user didn't notice that the stock rotated.
1.1.2>the tube had damage/wear on the section that is supposed to capture the buffer retainer

Permanent Fix:
Disassemble the lower.
Check the tube threads.
Check the forward/bottom section of the tube for damage/wear. Compare it with a new tube.
If you see damage to the threads or wear on the tube, replace it.
Reassemble and consider staking the castle nut and/or removable threadlocker.

[YourCoWorker]

I had a similar problem with a spikes factory assembled lower.
The tube barely captured the retainer and the retainer was perpetually cocked forward a little bit. I feared one day it would pop out.
I filed down the buffer tub a little at a time until I could get one more turn on the tube in the receiver.
Works perfectly.
I was inspired by a picture I saw of a factory buffer tube with an oval cut out in the retainer area, thereby capturing the retainer on, not only the back, but the sides a bit. Wish I could remember which manufacturer it was; It was a major brand name.

[Libertarian_Geek]

I had a similar problem with a spikes factory assembled lower.
The tube barely captured the retainer and the retainer was perpetually cocked forward a little bit. I feared one day it would pop out.
I filed down the buffer tub a little at a time until I could get one more turn on the tube in the receiver.
Works perfectly.
I was inspired by a picture I saw of a factory buffer tube with an oval cut out in the retainer area, thereby capturing the retainer on, not only the back, but the sides a bit. Wish I could remember which manufacturer it was; It was a major brand name.

I've seen what you're talking about. Something like this:



That's not a bad idea (IMHO).

[-k-]

Here is a quick install guide.

Screw the receiver extension in until it stops on the small part of the buffer retainer pin.
Back it off until it is in the correct position (less than one turn).
Tighten the castle nut to 30 ft-lbs.
Stake the endplate in two places.

[haus]

Mine looked like the picture prior to the failure. I also like the idea of getting that extra turn fromt he buffer tube. I could turn it in further but then my stock would have been mis-aligned. That would also allow me to keep the current tube, just work on it a bit. I did have the castle nut locked down with a wrench. 4 shots was not enough to loosen that so It must be the the buffer tube not coming over the retainer enough. Thanks for the help!

[haus]

Filing enough to get the extra turn seems to have done the trick. Thanks for the help!!! Now I need a chrono to figure out why my subsonic loads are not cycling the action.