I’ve assembled a few AR lowers in the past, but it’s not something I do often, so it’s very possible that I either didn’t do something, or didn’t do enough of something. Idunno yet.

There was an Anderson lower in the safe, begging for a parts kit (and a trigger upgrade) and this afternoon seemed like a prime time to start assembling.

I haven’t decided on an upgraded trigger yet, so I grabbed a standard lower parts kit from the box-o-parts in the shop. With a little help from an exploded diagram and “the 'Tube,” I got all the parts in place. I had to rob a second parts kit for one of the springs; thankfully I had another kit in the box.

After it was all together, I slipped an upper onto the lower. Turning the assembly upside down for a second afterward, I heard something rattling. I said to myself, “Self… that doesn’t sound right.” So I opened up the pair and found sure enough, “that ain’t right.”

The buffer retainer spring fell out on my counter, somewhat mangled. It took a little shaking of the assembly to get the buffer retainer itself to fall out.

The pin on top of the buffer retainer isn’t broken, though it looks very slightly bent. I’m not sure if that’s consequential or not. But why would those pieces have dislodged from their pocket to begin with?

Never seen this happen before!

Thanks, all.

ETA: According to Mr. Potterfield’s video I got the parts in place correctly. I left out the grease, but I knew I was going to have to lube everything before heading to the range with it.

The bend in the buffer retainer could be enough to dislodge the buffer and spring. I have owned a few Anderson lowers and some had issues- no threads for the grip screw, bolt catch area was out of spec and would not allow any bolt catch into it but I have never heard of an out of spec buffer retainer hole, although anything is possible. I would get a different buffer retainer and start there.

The buffer retainer pin and spring are themselves retained by the buffer tube. The bottom lip of the buffer tube should be overlapping the edge of the buffer retainer, right up next to the top post.

They would only be able to escape their hole if:

A) The buffer tube isn't screwed in far enough

or

B) The buffer retainer hole is out of spec.


The former is a semi-common mistake when assembling a lower. The latter is possible, but wouldn't be the first thing to check.

So try loosening your castle nut, remove your end plate, reinsert your buffer pin and spring, and then attempt to screw the buffer tube in one more revolution to capture the pin (if you can), then reinstall the end plate and retighten the castle nut.

Should end up looking like this:

^^^^

Thank you for the pic; that’s just about what mine looked like. I did wonder if one more revolution inward would help. Based on thread pitch, though, one more would cover about half of the pin.

Hoping I have a third parts kit in the box, that I can raid for that spring.

I did raid another parts kit for springs, and reassembled.

As Postimages isn’t working reliably lately, I’m working on finding somewhere else to host a pic.

Meanwhile, here are two pic links:
https://ibb.co/DD6xwc41
https://ibb.co/1J9QkGFr

- - - -
Pics (if they work):

Tinkering with it some more, things seem to be normal now. Maybe I simply didn’t have the buffer tube screwed in far enough on the first round.

Time to order replacement springs for these kits (and probably some spares) and get on with the build.

Thanks, all, for your help.

I opened up a rifle once only to have the buffer come spring part way out. The retaining pin was gone. Actually it was down in the bottom of the buffer tube, a little beat up. The tube was screwed in all the way, but SOMEHOW the retainer pin hole was stretched out, pushed forward and the retaining pin had managed to sneak out, and somehow get behind the buffer.

I used a punch and a hammer to tap the hole back closer to what it should have been, reassembled it and it never did it again.

vthoky, pick up an AR-15 Oops Kit like this one.

Oops Kit

Lots of companies offer them. That way you won’t have to raid a lower parts kit just for a spring.

This message has been edited. Last edited by: 2Adefender,

Great kit! Thank you!

That kit is a great idea. The only part I would add to that is the ball detent used in the rear iron sight.

quote:

Originally posted by 2Adefender:
vthoky, pick up an AR-15 Oops Kit like this one.

Oops Kit

Lots of companies offer them. That way you won’t have to raid a lower parts kit just for a spring.