The nub is off-center

offset retainer pin

Well I learned something today. I didn't know that existed, and now that I know why it exists I can see how I didn't know about it. Never had the problem that this intends to fix.

Thanks!

Yeah, it's a bandaid fix, covered in OP.

Guess I skimmed too fast

I do it all the time.

I always check a new build for this issue, though I've never had it happen.

When I bought my lower they were stored bulk in a barrel, about half the size of a 55 gallon drum, must have been a hundred of them in there. The packaging was different, some were just in a plastic bag, and some were wrapped with foam and then in plastic. The vast majority of them were the foam and plastic wrapped ones.

I did notice that the ones in just plastic had the hole milled farther back and had a rougher finish to the anodizing, and the grip screw hole was not threaded the whole way through.
The ones in foam and plastic were noticably smoother in finish and had the detent hole in the correct spot, don't recall about the grip screw hole on these.
I looked at a random sample of about a dozen of them.

Given the quantity of lowers in the barrel, I wonder if the plastic wrapped ones were old production with bad holes and the foam wrapped ones were newer production with the correct hole location. Not everyone that has Anderson lowers has this problem, so maybe it is just a bunch of older ones that were drilled wrong before they corrected the problem.

And I picked bad one and and I not happy about it, so don't think I am defending Anderson, just telling you what I saw.
The next  time I go to the store I will examine a few more of them.

My lower was in a plastic bag.  Bought a Anderson lower parts kit at the same time and the disconnector spring was missing.

Went through this a few years ago with a pair of Eagle/Armalite out of spec lowers. They were replaced with new/different serial number lowers.

The ATF will not change serial numbers on a Form 1. If your lower is replaced, you are SOL as far as the Form 1 is concerned.

I would try the off set pin or just remove the detent pin altogether, doesn't affect function.

Good Point.

I was really freaked out for the last half hour while looking at my stripped Spikes lowers as they have more threads to the buffer retainer hole like the problem lower. Then I measured distance from take down pin to the pocket and found out that the Spikes lowers have a pocket that was around .080" less deep than my other brand lowers. Hence, I do not think the extra threads will be a problem.

Don't feel bad, I bought a complete LPK from Anderson and the entire trigger assembly was missing

Update on my ticket with Anderson.  Received a call from someone in the shop and I explained my situation about the buffer getting chewed up.  Anderson said they would replace my lower and send it out in the mail today.  
I can live with that.

THAT'S HOW IT SHOULD WORK

There are more than quite a few Colt's like this.  I'd say about 1/4 of the hundreds, if not thousand, of Colt M4's I've seen have buffer peening.

THIS! I don't get it! People spend hundreds if not over a thousand dollars building a rifle and won't spend $10-$20 extra on a decent quality lower!

OK, I love cheap parts as much as the next guy, but not when its the ONE part I can't just up and re order and replace I spend a little bit EXTRA to make sure it is up to spec.

Especially on a SBR. You are investing $200 and almost a year wait at this point why skimp on quality?

Another update on my ticket with Anderson. Got my new lower today. Everything was in spec and went together smoothly. Turn around time for me was 1 day. All in all I'm happy but wish they would've offered to replace my damaged buffer. Oh well I didn't ask them to. Happy overall

That is how it should be handled (although throwing in a replacement buffer would have been better). For the OP, "fixing" (moving tolerance stacking around) by utilizing a non standard part is not "fixing" it. What they did was customize it. I'd be pissed and demand a proper mil spec replacement.
BTW, I'm a HUGE Anderson lower fan (their all I use) and have had FANTASTIC luck with 6 (now going on 8) lowers. Zero issues.
But if I ever received one like that (with retainer too far back), I'd raise hell about it until it was REPLACED (not "fixed", not customized", not repaired.... REPLACED).
As was mentioned, if it isn't to mil spec (as advertised), it's a faulty product (or falsely advertised) and they should REPLACE it immediately without question.

Thanks for the update.  Its good to know that Anderson stepped up and did the right thing.  My $50 Anderson stripped lower is just a sample of one,  but proved to be fully in  spec and nicely finished.

20 rds today with the modified Anderson buffer, seemed to work.  Saturday will be the test day, as I have 500 rds to burn.....

Well, how did it run through that ammo last weekend?

I'm surprised that they sent that buffer to you and didn't replace the lower.

Got out today with it.  Works fine.  Still a cheap fix for a defective lower.  I thought for sure they would of replaced the entire lower.

I am done buying Anderson Products.

My experience with Anderson service has been very good.
But keep in mind I shouldn't have needed that service if they offered well
made products. I will not buy Anderson anything again.

I ended up going back with the offset pin as it works better with a bump fire stock.  For some reason the modified buffer doesn't work correctly with a bump fire stock.

I am still very disappointed that Anderson didn't replace the lower.  Geez it would of been cheaper on them just to send me the modified buffer, rather than pay shipping both ways.  And we all know they have seen this problem before.  I bet their was an entire run of lowers with this out of spec reataining pin.

Buyer beware.  

I went ahead and went with the offset pin as well. Anderson just ignored my email all together.  Plus, I didn't want to strip down the lower just to send it in.  I have 3 of their lowers and this one was my panic buy.  At least there is a fix, and it's only a $15 lesson.  

That said, they lost me as a customer as well.    Thank you OP for putting up this thread.  I admit, that I learned something new, and to check for it on new builds.  

UPDATE:

400 rds today using the Anderson lower with the Offset Buffer Retainer pin works the best.  Anderson buffer mod acts like it has a mind of it's own.

Warning when looking for a lower beware of Anderson.  The lower should of been replaced.  Thumbs down for Anderson.

Exactly.  
 We should have a sticky with a warning about Anderson parts.
I've created numerous threads about their stuff I've gotten that's out of spec or just plain bad; take down pins too short, trigger/disconnect not working right together because of flaws, porosity in uppers and lowers, pin holes not drilled, mag wells not finished....and on and on. On about a dozen builds I don't think I had one go right.
Anderson always sent replacement parts, but even a little QC would have caught most problems.

Spike's is the 'cheapest' stuff I'll use now.

given any decent ambi safety is around $40 and up, what do you expect for a $50 lower.

I had an old Bushmaster that had the same issue but it was traded away many moons ago.  My Colt Factory SBR has the detent drilled off of the true 6 o'clock position by a millimeter or so, seems to be in the right place from front to back as there is no peening.

What is funny throughout this is while other people say they have had the same problem with other much more expensive brands... people keep bashing the one brand.

That said I have three Anderson lowers.  One has the retainer is just a slight tad off, works beautifully otherwise.  Offset pin will fix it and I can move on, big deal.

Well crap.
I just looked at the two remaining Anderson lower builds, one is fine, the other one looks like this:

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This one I had to get a replacement trigger and hammer- it wouldn't reset. I fired about ten rounds out of it trying to diagnose the problem. It was the cast stainless trigger/hammer set, they replaced it with a blued version that function tests fine, but I haven't had a chance to fire it yet with the new parts installed.
I'll send them an email and see what they say...

forgot to mention in my last post, I think many of the PDW style stocks omit the retainer pin to function with the shortened assemblies.  So there is a solution sort of, at least for the ones already SBR'd.

How is it a "thumbs down" for YOU accepting that "repair/mod/custom" fix they did? It was said on here, even before you accepted that "fix" that you should have demanded an in spec replacement. They probably would have if you told them that, however you went along with their "fix".  "Mil spec" should be within tolerance right out of the box. It wasn't (thus defective) and you let them take you for a ride (with their "fix"). While I understand they SHOULD have replaced it (as everyone suggested), you also need to understand you SHOULD have not accepted that "fix" and demanded they replace that faulty/defective receiver.
It's kind of like the Auto industry... even if they make a great product, defects happen and it's your diligence to nudge/push/force service (sometimes) to do the right thing. Sad that it's that way... but it is. You have to stick up for yourself.

just got my rifle back from colt performance in texas. they pretty much replaced the colt sporting lower with a colt competition lower because they were out of the sportings. bad thing is i went and did a quick dump of 3 mags and i think its still doing the marking thing to the buffer!!! not as bad as before but what the hell!! gonna run it some more and see how it does but at this point if its not severe im goin with the offset pin....

Point is I shouldn't to whine to them over a defective product. They saw it had a problem and made the call to mod the buffer. Nor did they tell me what they did, saying only a letter will be enclosed explaining the fix.  A stand up company would of replaced the lower.  Example my LWRC lower cracked, LWRC replaced the entire lower, gave me a free upgrade to ambidextrous and a better trigger.  Even the Anderson lower parts kit was missing parts.  Maybe Anderson doesn't understand QC ?  It is a like a roll of the dice if Anderson wants to replace or do a quick fix on out of spec parts. Nor did I feel like trying to get my point across to Anderson over this problem. Hell it took them 3 trys to get the return shipping label right. I have had better luck dealing with Chinese companies.  I stand firm on BUYER BEWARE on purchasing Anderson Junk.

I am wondering if Anderson lowers and parts are even made in the USA. Maybe they are made in Mexico as this would sound about right for lowers and parts being out of spec.  

sounds like a guy who never shopped for 922r compliance parts made in the USA...    Looks like we have passed peak quality for AR-15 parts.  Maybe AR-15 reputation will start to head down again like in the 80s and 90s when most parts were being made by fly by night operations and the damn guns wouldn't run right.

Buffer retainer pin isn't technically necessary.  It just makes disassembly/assembly easier.

I'd remove it and run without before buying an offset pin.

I understand. You just have to keep in mind that Manufacturing departments and service departments are two different animals. I haven't had any issues with Anderson products (yet), so I haven't used their service department. If I were you, I'd have emailed them that their "fix" was going back to them for replacement (not fix) as soon as I opened the box (actually, I'd STILL do it, even at the stage you're at now).
I get your frustration, and it sucks that it happened. It does happen with all manufacturers as well, and some of them handle their service MUCH better than Anderson did. When they don't... it's our responsibility to stand up for ourselves and MAKE them do the right thing (just as in my, common, auto industry analogy. We all know how difficult it can be to convince an auto dealer sales dept to acknowledge a "defect" (they almost always blame it on the user). We also all know how often we have to throw a fit and almost fight them to fix it on THEIR dime, but we do).
I'm not belittling your experience, I'm just saying you could have (and still should) hold their feet to the fire and demand they make it RIGHT (not "modded"). You paid for it, you deserve it the way it's supposed to be, not their "fix" of it.
But yeah, I understand your gripe, and would feel the same bitterness about it if that happened to me. I guess it would become principle for me at that point, that I'd fight them twice as hard just to make them do it right (and be a pain in the ass back to them haha).
I've had two experiences recently that irked me: Fostech ignoring requests (2 wks worth and 4 emails) to cancel an order (which got resolved when I had to threaten CC fraud involvement, then suddenly got my refund), and the dirt bag at FIST Holsters who also ignored emails for 3 weeks, then said product would ship 1 week later, then ignored emails for 3 MONTHS after. I had to also threaten CC Fraud with him as well, to which he replied I was a liar and a thief since I received his product. I then replied that I wanted the tracking number, was moving along with fraud case, and was reporting him to the BBB. He quickly replied he was sorry, that the tracking # (which he refused to give me) showed it got "lost" (sure) and offered me the product (again). I told him to stuff it (as well as calling him incompetent) and moved forward with ALL THREE actions. I'll never deal with that scumbag again.
So yeah... I feel your pain

OP, thank for the detailed description of the issue and all the follow up information.  
To me, the fix is unsat.  
Yes you have a usable carbine, my be good for a one and only but now you can not interchange parts or replace it easily.  You are tied to that buffer.

Personally, I stick with Aero lowers for builds.  The store front I go to lets me "inspect" and they will even look to make sure the lower is G2G.

IIRC, original AR15 design didn't even have one.  Big Army wanted one so the buffer didn't get lost

Yeah I bet that would be a real PITA without the buffer retaining pin.  For now the offset retaining pin is working fine.  

When I have the opportunity, I tell everyone about the out of spec lower problem.

So all those folks that were buying dozens of Anderson lowers before the election; I wonder how many of them are out of spec?  I mean you hedge for a crisis that was averted then you discover your investment is near worthless due to a lack of confidence in the quality of the product.  If I had a bunch of these like I know many due, I would check each one to make sure it was in spec or buy a bunch of the offset pins.

I've read enough negative shit about Anderson lowers I don't think I would ever buy one.

FWIW on the $15 offset pin, that is out the door (they don't charge extra to ship a tiny piece of nothing even though they ship it in a huge padded envelope) and it took me two days to get it.

Good, I hope more people think the same. More for me (8 lowers with 0 issues). I laugh at people that pay more (and rub it in their face).

Good for you. I'll stick with brands that don't have a shitty reputation.

I would rather pay more for a better lower that doesn't have issues.  The internet is full of people complaining about Anderson lowers being out of spec.

I wouldn't say there are a ton of complaints. You, yourself, didn't even know of the issue you had until after the fact. Also factor in that Anderson probably outsells (both themselves AND the others they supply to) any other brand out there (for lowers) by double digit percentages and the scope of complaints seem MUCH more reasonable (and even then, I'm not aware of many complaints of them. The grip screw depth is a "known", and now this, seemingly rare, issue). But to each their own (as said, I'll continue to use them, and only them, as I've had nothing but luck with them and they happen to be the lowest cost out there ).
And as I said before, if you had stood up for yourself you'd have a perfectly working lower (to spec) and it wouldn't have cost you any more (and you can still do so. Just tell them it's not acceptable and demand they replace it. If not, demand a refund. Stick up for yourself).

There are plenty of complaints over more than one issue- it's an obvious lack of quality control over all. I built 4 of their lowers and had problems with two of them- the bho slots were too thin and ended up binding the BHO's so that the bolt would not lock back on the last round fired. I was able to get it fixed and the guns work fine but I won't use them again.

I understand saving money- there is no reason to pay more for something than you need to- but to me, you're only talking $30 or so between the cost of an Anderson and a better lower. It's a LIFETIME purchase, $30 is of very little consequence in that case. If $30 is the difference between having an AR and not having an AR.....maybe that person doesn't NEED an AR?

Some folks buy lowers in bulk - $30 is more than half another Anderson lower.  I saw them @ the show this weekend for just over $50/ea.

And EVERYONE needs an AR.  It's the militia's weapon, and you are part of the well-regulated Militia, aren't you?