bought this lower the other day for a first build, and the damn buffer pin wont stay in at all.  it looks like they do a cut out so they can put their buffer tube in deeper and failed to thread it all the way.  I dont have the castlenut wrench so now I'll have to go buy one.  is this typical of DPMS?

Looks like you need to purchase a new tube.

I'm not sure if its common with DPMS to do this but somebody tinkered with it only to make it worse.

Get a new tube and try it again.

that ain't right at all

You can't take it back?

Looks like some Bubba smithing. If you screw the extension in too far, you may not be able to close the upper receiver. It appears they wanted to screw it in deep, but it was binding against the retaining pin. So they Bubba-smithed the extension to relieve where it binded.

it looks to me like on either side of the buffer pin notch the metal is shaved or chipped away make a complete hole for the retainer to pop free of the buffer tube.

you need a new buffer tube. i have seen this once,the buffer tube holds the detent in place.i have a new one for sale fits an m-4

Centerfire systems has a buffer tube for $24.99 (cheap option )

It's probably a cheap chicom tube, but it will work.




Squig

Quoted: bought this lower the other day for a first build, and the damn buffer pin wont stay in at all.  it looks like they do a cut out so they can put their buffer tube in deeper and failed to thread it all the way.  I dont have the castlenut wrench so now I'll have to go buy one.  is this typical of DPMS? img294.imageshack.us/img294/9551/p7130084st7.jpg

Was this a complete lower or a kit put on a stripped lower?  The cut out is there in the tube for that the pin part of the buffer retainer came come up and as a partial indexer for the stock being squared to the receiver.

You make reference to not threading all the way?  Are you talking about the tube of the recevier?  There should be plenty of thread on the tube left.  The receiver has a ton of thread in front of where you are.  So what it look like you need to do is loosen the castle nut, then turn the stock and tube in one more turn.  As long as you can turn it a full turn and not make the detent stick.  If you can, then at the back of the receiver see if you have tube sticking through that block the upper from coming down.  If you do lightly file it back or pull the tube off, File/sand back, reinstall the tube.

It really appears like it was put on one turn too lite and the detent pushed off the little bit of metal that was holding it down.

What if you put it to a belt sander and shave the entire end off square till that cutout is gone? Saves you a few dollers on parts and shipping.

Although here are two other DPMS receivers for contrast.  Both of the tubes though are ACE tubes with no notch in them.

You can either fit the tube you have to your receiver, or replace your tube. Fitting may require some filing and sanding. Turn the buffer tube in 1 full turn until the buffer pin is secured. File and sand the tube so the upper closes. This shouldn't happen in a new gun.

Quoted: Who ever ground on that receiver extension knew absolutely nothing about how the buffer retainer functions.

That's where I'd put my money. I'm guessing the "dealer" assembled the lower not realizing the pin is captive.

Note on this photo... there is a half thread on the bottom of the tube that is ground away on the upper portion of the tube.  Can you see it on each side?

This is correct.

Many times a carbine tube is cut straight across the tube.  Then, when it is threaded into the receiver to properly hold down the detent, as you can see in this photo, with the tube almost, but not quite touching the "tit" on the detent, then the threads protrude at the top.  That prevents the upper from closing.

So some dufus unscrews the tube one full turn.  Now it is back enough to allow the upper to close, but does not sufficiently hold the detent.

The correct thing to do is simply grind back that upper thread, easily done on a bench grinder and then dress off the rough spots with a wire brush.

Better quality carbine tubes come with that upper thread already trimmed back.  And from the appearance in this photo, this was one that was properly shaped to begin with.

Get a new tube and fit it as I have just described.


In the next photo, this tube is not properly installed.  It does not thread in enough to properly capture the detent.  The person that installed this tube was afraid it would protrude too much at the top and bind with the upper receiver.  He was correct.  As it is, it may work for a short while, but soon a little wear on the edge of the tube will allow the detent to get loose.  FAIL!




This next tube is not properly installed, either.  It is threaded in enough to capture the detent, but the top thread of the tube protrudes past the upper receiver where it will bind and wear on the upper receiver.  FAIL!




These two improperly installed tubes are not the fault of the DPMS receivers.  They would be that way in any receiver.

Are those photos of Ace stocks?  The Ace tube is cut with a longer lip on bottom.





What they are is the result of poor installation.

this was a DPMS complete lower receiver.  any failure is their fault alone.  it does have the filing done already and I think it will work fine with one more turn, it just pisses me off they let it through like this.

Quoted: In the next photo, this tube is not properly installed.  It does not thread in enough to properly capture the detent.  The person that installed this tube was afraid it would protrude too much at the top and bind with the upper receiver.  He was correct.  As it is, it may work for a short while, but soon a little wear on the edge of the tube will allow the detent to get loose.  FAIL! farm4.static.flickr.com/3292/2668505017_cedd403286_b.jpg This next tube is not properly installed, either.  It is threaded in enough to capture the detent, but the top thread of the tube protrudes past the upper receiver where it will bind and wear on the upper receiver.  FAIL! farm4.static.flickr.com/3079/2668505375_9319caa7e4_b.jpg These two improperly installed tubes are not the fault of the DPMS receivers.  They would be that way in any receiver. Are those photos of Ace stocks?  The Ace tube is cut with a longer lip on bottom. www.riflestocks.com/images06/AR/m4s.ssar.jpg What they are is the result of poor installation.

Actually I grabbed the wrong photo and both are of the same lower vs. two different lowers.  MOST of the ACE tubes are done with the longer lip.  That one is a fixed length rifle buffered skeleton stock so it is not cut that way vs. say the SOCOM.

So as you noted in the second photo it does capature the detent and as you didn't in the first it actually doesn't protrude into the upper.  It runs just a hair short of flush.  But it is more or less like an A1/A2 tube.

Then again I admit it's hard to tell from a picture and angles certainly change how things look.  

I don't have any improperly assembled AR's but thanks for playing.  

I have a buffer tube that has a similar notch to the one you originally pictured, except that the notch is straight and not flaired.  It looks to me like you might be able to put one more turn on the tube and the remaining portion of the notch will center on the pin of the buffer retainer as it should.

Just make sure that once you make another turn that there is no metal from the buffer tube extending past the top of the receiver threads that would prevent you installing the upper.

save yourself some time, that tube is....for the most part toast.  Best bet to take it back, if you can, and get a new one.   If not then you can find them online and change it out.

which direction do I turn the castle nut when looking down at a shooters point of view of the weapon?  it seems like it would be counter clockwise, but it wont budge.  I just bent my CAR wrench trying to get it off.

I just installed a DPMS stock for my son last night, wish my dad had built me an AR when I was 14, it has the same notch.  I gave it one more turn and tightened the locking ring, works like a charm.  Like another member said, "Give it another turn".

Semper Fi

Quoted: ........................ A properly installed receiver extension, securing the buffer retainer........... img.photobucket.com/albums/v489/Metroliner/BufferRetainerPin800.jpg

Stake that castle nut.......

You know I got the same problem with my DPMS lower. I took the A2 stock off and put a Bushy M4 stock on. If I tighten some more my upper would not go into lower, So I just had to live with this (pics below) haven't shot it yet so don't know if it will work. It does keep the pin down though. Any ideas on what I should do? Its a fixed stock so i dont think i can change out the tube.

well I bent my CAR wrench trying to get it off.  any suggestions on actual removal?

that's exactly what i ended up doing, good investment