I drilled the bolt retainer back too far and it contacts the buffer before it hits the bolt carrier. What kind of problem is this going to cause besides the little impressions in the buffer? Heres a pic to help clairfy any questions. The inpressions look deeper in the picture than they do on the in person.
 http://www.hunt101.com/watermark.php?file=552/32211ar15_027-med.jpg

I dont think it will work because the buffer holds the carrier tight when a round it chambered.

TO CORRECT THIS PROBLEM
MILL A SLOT IN THE BOTTOM / REAR OF YOUR BOLT CARRIER

THIS WILL ALLOW IT SOME SPACE SO IT WILL NOT PUT DENTS IN YOUR BUFFER

WILLAIM

I haven't shot it yet with the retainer in but it pick up the rounds and locks the bolt just fine. Even when I feed a round in by hand the bolt lock shut if I only pull it back 1 1/2" - 2" and let the charging handle "fly".

William, you must have been typing the same time as me, the bolt carrier already has a slot milled into it. The problem is the retainer pin wont let the buffer move foward enough. When I close the upper to the lower from what I can see the rear or the carrier hits the buffer but apparently there is a slight gap in there.

What is that imprint in the ring portion of your lower at the 12 o'clock position?  

I  hope that your carrier key is not slamming against your lower before the urethane bumper on the back of your buffer makes contact with the back of your buffer tube.  If it is, you are going to get a real surprise when firing your rifle one of these days.  The rear of your rifle will possibly break off.

I just operate mine without a buffer retaining pin. Just be careful when you open it up, and everything works fine.

You need to move the hole forward. It's supposed to be on a 6 degree angle, also.  It also looks like your rear tang is too thick and the buffer tube doesn't thread far enough forward.  When the upper is closed the buffer should not be touching the buffer retainer.  

rj

Ok, I see a couple of things in that picture:

1) There is a carrier key shaped yield mark in the top of the ring.   This may have happened several ways, but if the key can strike there when firing your buffer or tube is out of spec.

2) The buffer tube does not appear to be screwed all the way in.  This could be part of problem #1 above, allowing the buffer to travel farther before contacting the bottom of the tube.


The marks in the face of the anodized buffer appear to be chatter marks, and may have been there for a long time.

To check the location of the buffer detent, assemble the tube/spring/buffer on the lower, and place a straightedge across the top third of the buffer.  It should protrude slightly from the face of the receiver ring, allowing for a slight preload on the bolt carrier assembly when the weapon is assembled.

Colt (and many others) drill the detent hole at an angle, so that they miss the top of the ring with the drill body.  Some manufacturers used a reduced shank drill, and went straight down.  Still others cut a small portion of the ring away, and drilled straight down.  

If you need to move the hole, you should use an aluminum plug to fill the old hole first.  The best thing to do is bore the existing hole oversize to about .375, then press fit an aluminum plug in the hole.  Done carefully, this repair is almost invisible & can be anodized.


Lem

When I drilled the hole I drilled it back too far. I did get the 6* angle. Also when I drilled it the bit walked slightly back and made the inpression it the top of the buffer threaded area but that is cosmetic. The marks on each side of that is from test fitting before any pivits were drilled and are nothing to worry about either. The rifle fires fine without the buffer pin in place. As far as the retainer pin being off I bet if I went foward .020" everything would have been fine. I was half thinking if I came up with an offset pin that would fix the problem. It would be a PIA to make with the tools I have but it would fix the problem. Any other ideas besides leaving the pin out, it is kind of handy or redrilling.

Anotherred, I'm glad that you posted this. I just built up a AR from a 80% er and it got me thinking about mine - I've got the same problem as you ... not the drill mark, but the horizontal marks indicating that the carrier key is making contact with the receiver ring.
It seems to me that since the "ding" in my receiver is only about .010 to .015 deep, that it's not off much, but enough to screw things up. I agree with Lem, especially point #2 - the buffer tube not being screwed in all the way, allowing the buffer to travel farther before contacting the bottom of the tube.
I like the idea you had about the "offset retainer pin". It would allow for at least one more turn in on the bufer tube - the extra .015 to .020 needed to keep the carrier key from making contact. I also thought that there is enough material to remove about .020 or more from the back of the carrier key before running too close to the rear allen head screw in the rear of the key. Good luck fixing it - I guess it's back to the drawing board for me too.

joedoran

Just take your bolt carrier and jam it back in the buffer tube and see if the carrier key hits.

You could always just machine a steel  spacer that would fit into the back of the carrier and lengthen the carrier just enough to solve all your problems.

rj

I took the spring out and put the bolt carrier & buffer in the buffer tube and they bottom out with room to spare. I wonder if I remove the metal on the buffer if that would have a negative effect. The ring would only have to be .003 deep and .07 wide. I'll probally try to fab an offset pin first and see how that turms out.

You will have to do something to keep the pin from rotating.

rj

I think that the spring pressure would keep if form turning. If not a little notch or step on the buffer side would keep it positioned properly.

The location of the hole for the buffer retaining pin is too far back so the pin is stopping the buffer rather than it resting up against the carrier. You should be able to see this gap between the buffer and the carrier when you close the upper on the lower. Normally, when you close the upper, the carrier strikes the buffer, pushing it back so that it doesn't hit the pin.

There are 2 remedies to this. One, is to stick/glue/screw something on the front of the buffer. Thick/sturdy cardboard, a piece of metal, or anything that is slightly thicker than the depth of the indent made by the pin on the buffer. Cut this piece into a circle and cut it smaller than the head of the buffer, so that when it is in place, the pin does not contact. Turn the buffer to make sure the pin doesn't touch this spacer on any edge.

A 2nd remedy is to cut a shelf around the edge of the buffer. The height of the shelf be high enough so that the retainer pin can slip beneath it. The shelf should also be slightly deeper than the depth of the dents in the buffer.

What either of these remedies will do is to allow the center area of the buffer to push up against the carrier. The shelf will also allow the pin to slide into it so it won't damage the buffer any more.

Or, you could remove the retaining pin and spring and not use them. You'll just have to remember to hold the buffer and spring in place whenever you break open the upper.

I had the same problem on one of my 80% and used option #2, and it works perfectly. If you have trouble envisioning this, let me know and I can post a pic tomorrow.

neilfj, I was thinking along the line as your second idea also. I appericiate your help with this slight yet annoying problem.

Quoted: i removed all the buffer retainers from my guns. i have had more than one break over the years causing a NASTY jam in the gun. just remember it's not there when you clean the gun and you will never notice it missing.

It would be easy enough to grind a relief in the buffer tube that would allow you to put in a retainer and spring when you opened up the rifle.  This would simplify the cleaning so you wouldn't have to be holding the buffer. Or I guess you could just not cock the hammer and let the buffer rest against that, hmm.

rj

I'm having the same problem with mine and would like to see a pic - THANKS!

joedoran

Quoted: A 2nd remedy is to cut a shelf around the edge of the buffer. The height of the shelf be high enough so that the retainer pin can slip beneath it. The shelf should also be slightly deeper than the depth of the dents in the buffer. What either of these remedies will do is to allow the center area of the buffer to push up against the carrier. The shelf will also allow the pin to slide into it so it won't damage the buffer any more. I had the same problem on one of my 80% and used option #2, and it works perfectly. If you have trouble envisioning this, let me know and I can post a pic tomorrow.

[edited out a suggestion already offered... next time I will read the whole thread]

WHAT TYPE OF 80% LOWER IS IT?
IT LOOKS LIKE A KT TOOL ?
IS IT THE NEW MODULAR ONE?

WILLAIM

Its a KT, but just the regular one. William I will probally order one of your lowers when I decide to to another one. The reason I went with the kt 80% is all the hole were premarked and I haven't even held an AR before. The project was almost too easy. Now that I have a lower for a reference I'll be able to take something a little more difficult on next time. I dont know if I should post this but heres some nice pictures look hereof the modular one.

joedoran;
I'm out of town until Monday, so I'll post a pic then.

Thanks neilfj.

Joe

Quoted: joedoran; I'm out of town until Monday, so I'll post a pic then.

Joe, Here are the pics of an 80% lower that I had the same issue with. The buffer has been trimmed around the edge so that the retaining pin doesn't interfer with it. This extends the center area of the buffer so that when the upper is closed, the carrier pushes the buffer slightly back into the extension tube. You trim the edge of the buffer just high enough so that the pin slips under the center section of the head, and just deep enough so that the center of the buffer touches the carrier when you close the upper. Trim around the entire circumference of the buffer head so that the rotation of the buffer won't be an issue.

Thanks Neiljf for the pics - Now I know how to fix it.

joedoran

Awesome, I was thinking of that as a fix but wasn't shure if it would work. Thanks for that pics.