Okay a buddy of mine put together his AR kit lower today, and it was pretty tight when trying to rack the bolt back.  At one point the bolt would only go back about an inch and would not fully rack backwards.  Could not get it to move other than an inch.  We decided to disconnect the lower and upper and what do we find?  It seems the buffer has bypassed its detent pin and sprung outward hitting the hammer.  It appears the detent pin bent forward and now will not retain the buffer.  Does anybody know what could have gone wrong other than a screwed up detent pin?

OK, even if you slapped the upper and the lower together without a detent in, the buffer would only go ar far as the bolt carrier.  How did it manage to hit the hammer?  You leaving something out.

He means after they removed the upper.

Did he have the buffer tube all the way over the buffer detent to hold it completely in place.  It should have been right up to the edge of the protruding pin portion.

Did you guys put the spring in the buffer detent? I have heard of this happening but the buffer assemby is so basic, it must be a simple problem. No detent spring, bad detent or spring. Is this an 80% lower you guys finished? Sometimes I have noticed on 80% lowers that the hole for the detent is not deep enough or worse yet, drilled too deep which in that case.....you're screwed and pooced the lower. I'd pull it apart, check the buffer, detent and spring. I'd pop in a new detent and spring and see what happens. The buffer when the rifle is closed cannot hit the hammer, only the carrier. If it hits the carrier, the detent or lower is pooched and it's dangerous. I have seen this, it's not all that un-common.

Yes.  This happened to me.  I put a kit together and had this problem several times.  Here is what is happening.  Your friend probably has a CAR stock.  He installed the buffer tube to rest up against the buffer detent pin.  He should have submerged the detent and turned the tube one more time. Yes.  I know it looks like the detent "nipple"  wont hold the buffer back but it will.  Here is what you need to do.  Go to [url]http://www.brownells.com[/url] and order FIVE buffer retainer pins @ $1.50  (item 231-000-107) Then replace the pin with one of your new ones and bring the rest to the range.

If I'm wrong, someone here will correct me (its a forum you know) but if I'm right and this works, you will start to feel guilty that you haven't gotten a Bronze Membership to this forum.  [coffee]

Yep, if it is a CAR stock, which I failed to rmember, this could very well be the issue. It is a little mind boggling that that little pin will hold the buffer, but it will. That with the firing pin retaining pin are the two AR-15 designs I never understood. But hey, 35 years and countless wars cannot be wrong.

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Not true at all. You can drill the detent hole completely thru the lower if you want and it won't bother the operation of the rifle, other than having to be careful when separating the upper/lower so that the buffer doesn't fly across the room.

Yes it was held in completely by the detent that protruded.  We even pressed the detent pin up and down to make sure that it had spring tension and pressed the buffer tube in and out to make sure it would be retained.  

The spring was installed.  But, what is a 80% lower is?


It is a standard A2 stock.  But the tube was installed in according to rest against the detent pin.  The detent pin was not submerged and then the tube turned.  It looks like if the pin was submerged then the tubed turned one more time, the detent pin would be under the tube and therefore useless, am I wrong in my observations?


 

Yes you are wrong in your observations. Did you happen to notice that there is a shoulder on the buffer tube that screws flush against the back of the receiver. When you install this part. You put the buffer tube in almost tight, then you put the spirng and buffer retaining pin in and hold it compressed against the spring. Then screw the buffer tube in till tight against the receiver, this will catch on the shoulder of the buffer pin, leaving just the smaller diam tip exposed. The buffer pin only does something when the receiver is opened the rest of the time the buffer is against the back of the bolt carrier and nothing touches the buffer retaining pin.

the interesting thing was that my own rifle's detent pin looked the same asmy friends and I have put at least 600 rounds through mine without a hiccup or problem.  I noticed there is a small groove cut out of the bottom towards the rear of the AR bolt carriers which provides clearance for the detent pin when the bolt is cocked back.  After the detent pinw as bent, I placed the bolt into the buffer tube to check the clearance bettwen this groove and hte pin.  I noticed even after being severely bent, it was almost touching the bolt.  So I checked the groove in comparison to my own bolt and they "appeared" to have been cut the same distance, depth and width.  With this in mind, it definetly either sounds like as some have mentioned the Buffer tube needs another turn, or the detent pin was out of spec.

I didn't notice a shoulder, but it seemed obvious to me when I screw in the buffer tube that one turn too far and the pin of the buffer retainer would not protrude properly, and one less turn would not hold the retainer at all. That's what it seemed like at the time at least.

Um, since you didn't mentioned what kind of stock I must ask:  you aren't using some kind of stock that utilizes a carbine/collapsing stock length tube and a full A2 stock length spring that may have been so strong that it battered the retainer pin, are you?  Since your pin is bent forward, I wonder if it took a beating from a buffer spring that was too strong.  If the buffer detent/retaining spring was missing or weak, it may have only pushed the retainer pin up just a little so the buffer hit the very tip bending it forward.  I'm going with the missing/weak spring for buffer retaining detent/pin theory.

Edit:  Ack!  Sorry, your right, you did say A2 stock and spring, I missed that.

sorry, thought I alreayd stated what type of stock it is.  A2 with A2 buffer tube and spring.  No tele. components in it.

Who makes the stock,if the full size A2 tube were not screwed in flush to the receiver I dont think the stock would fit flush there would be a gap and you would be able to see the rear take down pin spring because the stock holds that in,even with my clapsable bush when I changed the tube the bushy extension has a lower lip face that makes it impossible to over turn,when the tube stops against the detent you have to back it off a inch or so then tighten the ring but on an A2 there is the shoulder that someone mentioned maybe thats off and it wont screw in flush.

The buffer retainer only retains the buffer when the upper is off the lower. The buffer rests against the rear of the bolt carrier when the rifle is assembled.