I was out with a friend this morning to do some plinking and for him to get a chance at some trigger time on a couple of new toys he had picked up.  One of those was an RRA carbine that he had just bought and then installed a collapsing stock on.  He's new to ARs and I wanted to be on hand to help him break this one in.

So we finally get set up on the line and put some targets downrange.  He seats a mag but then notices the bolt doesn't fully go home.  I hadn't noticed him riding the charging handle but asked him to drop the mag and check the chamber before proceeding.  Nothing looks too amiss after this so he loads up again but once more the bolt will not completely close.  

Now I get involved.  I drop the mag and cycle the bolt on an empty mag well and the bolt goes home.  I then decide to open up the gun and take a look at the insides to get an idea of what's happening.  The first thing that happens as the recievers separate is that the buffer spring shoots forward out of the buffer tube!

I find the buffer retaining pin in the bottom of the lower reciever and the buffer retaining pin spring wedged under the bolt carrier.  Worse yet there is bright, worn aluminum in the threads of the reciever extension and a couple of small chips of aluminum there from where the threads have been damaged!.  This damage is on the inside of the reciever and nothing is screwed into those threads.

We figured he must of not replaced the buffer retaining pin detents properly or something.  My buddy is pissed, but I told him not to sweat it too hard - in the worst case a stripped lower isn't all that expensive.

So what do you folks think happened?  Is his lower trashed or is there hope?

Replace the spring if damaged and screw the buffer tube in another rotation to see if it is enough to hold the pin in place.  Sounds like to stock tube was not screwed in enough to hold the pin down.

Sounds like the buffer tube wasnt screwed in far enough to capture the retaining pin and spring.  As long as the hole that the retainer and spring sit in isn't FUBAR'd and the thread damage on the receiver is limited to the inside of the receiver, you should be able to properly install the buffer tube and go.  There will always be a nasty reminder of what happened inside the receiver, though.

Is a pic possible?  It'd help alot.

Good luck with this.

Quoted: Sounds like the buffer tube wasnt screwed in far enough to capture the retaining pin and spring.  As long as the hole that the retainer and spring sit in isn't FUBAR'd and the thread damage on the receiver is limited to the inside of the receiver, you should be able to properly install the buffer tube and go.  There will always be a nasty reminder of what happened inside the receiver, though. Is a pic possible?  It'd help alot. Good luck with this.

That makes sense.  I've installed folding stocks before but forgot that it's the buffer tube that keeps the retaining pin in place!

You guys have a good idea of the situation, the damage I saw was on the reciever side of the retaining pin hole, not the stock side.  I'm not sure if the retaining pin hole was misshaped, however.  Thanks!

Quoted: If that happened to one of mine,  I'd bead blast the whole thing clean, get the damaged area welded up, remachine as necessary, retap the buffer hole, and then get the lower re-anodized.      If the damage wasn't so severe, I'd just do spot touchups and hopefully not have to reanodize it. CJ

I've had the same thing happen to one of mine. Once I got the tube screwed in far enough I used some aluminum black to return the receiver to a proper color.

Welding and machining would be WAY WAY WAY too much work for a lower. If it was that damaged I would chop it and replace with a new one.

Quoted: Quoted: If that happened to one of mine,  I'd bead blast the whole thing clean, get the damaged area welded up, remachine as necessary, retap the buffer hole, and then get the lower re-anodized.      If the damage wasn't so severe, I'd just do spot touchups and hopefully not have to reanodize it. CJ I've had the same thing happen to one of mine. Once I got the tube screwed in far enough I used some aluminum black to return the receiver to a proper color. Welding and machining would be WAY WAY WAY too much work for a lower. If it was that damaged I would chop it and replace with a new one.

Keep in mind you may be talking to people that would karate chop you in the jugular to beat you to a piece of unclaimed brass...

Some folks, with the right tools, will go through hell and back to save part of their gun... nevertheless a lower!

I'd say it would be worth the effort 95% of the time.

- BG

Quoted: Dark, Whose buttstock?

Yet another one without the timing lip.

Quoted: Dark, Whose buttstock?

I saw a familiar coiled snake on the side, so the answer is Bushmaster.

If you have a 7075 forged upper, DON'T TRY TO WELD IT.  7075 does not weld.

My guess is that the thread was damaged when the retaining pin got loose.  The AR would function just fine without the buffer/spring assembly retaining pin.  It is there to hold the buffer/spring unit in place while the upper is open and during reassembly (an inconvenience rather than functional issue.) If this pin breaks and wedge itself in the lower, the rifle would be inoperable.  A few of the 3 gun competitors now run their ARs without the buffer retaining pin just to avoid the aforementioned failure.

Quoted: My guess is that the thread was damaged when the retaining pin got loose.  The AR would function just fine without the buffer/spring assembly retaining pin.  It is there to hold the buffer/spring unit in place while the upper is open and during reassembly (an inconvenience rather than functional issue.) If this pin breaks and wedge itself in the lower, the rifle would be inoperable.  A few of the 3 gun competitors now run their ARs without the buffer retaining pin just to avoid the aforementioned failure.

I think that's spot on, B52.  Those 3-gun folks sound a little overboard, eh?  Maybe a delrin pin might be the ticket for them, something that's strong enough to retain the buffer but soft enough to avoid damaging the threads if it pops?

Quoted: If that happened to one of mine,  I'd bead blast the whole thing clean, get the damaged area welded up, remachine as necessary, retap the buffer hole, and then get the lower re-anodized.      If the damage wasn't so severe, I'd just do spot touchups and hopefully not have to reanodize it. CJ

Thats alot of shit to do for a nothing special receiver. I could see doing that for a registerd receiver but not for a RRA. mongo001 had the right idea.

Quoted: Quoted: If you have a 7075 forged upper, DON'T TRY TO WELD IT.  7075 does not weld. I assure you, it DOES.   When I milled out a receiver from a zero percent forging, I made a mistake or two that I had welded up by a local welder (who, incidentally, is certified by Nasa to weld on space hardware including shuttle parts) and I assure you,  the welds are fine.    The external appearance of the welds wasn't the classic 'row of dimes overlapping' but underneath, you can't tell when you machine it.   However, the repaired spots did anodize differently.  There's a difference in the appearance of the black anodized finish in those spots. The big mistake I made, and that had to be rewelded, was that I got the buffer tube hole off center and had the whole internal bore built up and then I remachined it.  THAT time, I got it perfect. CJ

That is still ALOT of BS to go through when lowers are so cheap.

If I understand correctly you just need two new parts, pin & spring, if the threads aren't too chewed up. Post pics if possible.

Go to www.rbprecision.com/rock_river_arms_ar15_rifles.htm and order parts #108 + #109 for a total of $1.20.

Also there is a good tutorial @ www.rbprecision.com/rb_precision_ar15_performance_tips_.htm w/ pics for installing a stock.

FB

Quoted: Maybe in your world,  100 bucks (or more) is cheap,  but not in mine.   But then again, the Grand Canyon was dug by an ancestor of mine who dropped a nickel in the sand one day and dug to try to find it! If you think a new lower is cheap,   I'll make you a deal:  I'll buy every damaged lower receiver you can send me for a flat rate price of 25 bucks apiece,  all day long.   As long as they're not illegal,  like unregistered MG lowers. CJ

How much would it cost to get a receiver welded, milled, reanodized, and refinished... Not doing it yourself on your own equipment but having this done? I am just curiouse...

ETA: I have never broke a lower receiver so you are SOL...

Quoted: Quoted: If that happened to one of mine,  I'd bead blast the whole thing clean, get the damaged area welded up, remachine as necessary, retap the buffer hole, and then get the lower re-anodized.      If the damage wasn't so severe, I'd just do spot touchups and hopefully not have to reanodize it. CJ Thats alot of shit to do for a nothing special receiver. I could see doing that for a registerd receiver but not for a RRA. mongo001 had the right idea.

even a "special" receiver is not worth the hassle, unless it was simply a collectors piece by virtue of its production date, it would be easier to just reman the number to a new lower as a repaired item, hell lowers are getting cheaper and cheaper each day, if you had more than an hour in the repair, the shop time cost would justify a new receiver.

but the, his gun is not really hurt from the description, just another case of not really knowing what he was doing.

Quoted: Quoted: My guess is that the thread was damaged when the retaining pin got loose.  The AR would function just fine without the buffer/spring assembly retaining pin.  It is there to hold the buffer/spring unit in place while the upper is open and during reassembly (an inconvenience rather than functional issue.) If this pin breaks and wedge itself in the lower, the rifle would be inoperable.  A few of the 3 gun competitors now run their ARs without the buffer retaining pin just to avoid the aforementioned failure. I think that's spot on, B52.  Those 3-gun folks sound a little overboard, eh?  Maybe a delrin pin might be the ticket for them, something that's strong enough to retain the buffer but soft enough to avoid damaging the threads if it pops?

The reason for some of the 3 gun guys to run without this retaining pin is that if it happens to pop/break in a stage of a big match, then it's over for the high placement.  You know why DPMS is making steel charging handle? Because Jerry Miculek (sponsored by DPMS) bent the std charging handle in the 2002 national match during a gunning-and-running hosing stage, upsetting his chance to win.

Quoted: Replace the spring if damaged and screw the buffer tube in another rotation to see if it is enough to hold the pin in place.  Sounds like to stock tube was not screwed in enough to hold the pin down.

+1

Well, let me throw in my 2cents.  

Actually, it sounds like there is a minor mating problem between the upper and lower.  Is it possible that the upper is too far forward on the lower which allows the buffer to slam into the spring loaded buffer retaining pin when you fire?  That would shear the top of the buffer pin right off after a couple of rounds and you'll easily end up with the scenario you've experienced.  

Check it this way. Mate the lower to the upper on the front pin and as you close the rifle on the rear pin, and if your two halves are properly mated, you'll notice the the buffer just kisses the rear of the bolt.  That kiss keeps the buffer from slamming into the pin every time you fire.  The retaining pin is just there to keep the buffer in place when you open the rifle for maintenance.  

I discovered this problem in my own project AR when I first built it.  I had an large hole SP1 slab side upper mated to a small hole lower.  I had the sleeve in the large hole to reduce its diameter but it's and eccentric round sleeve and I didn't have it turned correctly.  So, as I lowered the upper to the lower, there was a small space between the rear of the bolt and the front of the buffer.  Therefore, every time I fired, the bolt would slam the buffer back properly, but when the buffer returned from compression, the only thing keeping the buffer back was the spring loaded retaining pin.  After a few rounds, the buffer sheared off the top of the pin and if fell out on the table.  When I opened up the rifle to inspect it, my buffer and spring flew forward, too.  Fortunately there wasn't any damage that was noticable.  It took me about two days to figure out the problem.  It all comes down to the "kiss" I mentioned earlier.  So, reassemble the rifle as it comes down on the rear, notice if the bolt touches and slightly moves the buffer back off the pin.  If it does, then all bets are off.  If it doesn't, however, you'll have to check to see if you have forward to backward movement of the upper on the lower.  If it does, you'll have to sleeve the front hole of the upper so that it's properly positioned on the lower and the bolt does touch the buffer.

Sorry for being so long winded.  This was a frustrating problem I had and I was thrilled to finally figure it out.....but only after I'd ruined three retaining pins!

Rome

Quoted: I had that work done (weld, remachine, and reanodize) done for a total of 25 bucks.   The welding was done by a friend as a favor,  I did the machining myself,  and the anodizing was cheap because I got it in on another batch lot being done to the same spec, and also there was a favor involved.  (The anodizer owed me one because I'd brought him a fair amount of business.) Your mileage may vary.   CJ

There are also people on this board who have built AR's for as low as $150.00 total cost but this is far from the norm.