Gunsmithing Buffer Retaininer Pin and Spring Problem

[fx77]

Shooting an Alex Arms Upper in 6.5 Grendel
and a Bushmaster Lower. After about 5 rounds- all of which feed fine, the BCA jams. After opening the rifle the Buffer retainer pin and its spring are found under the bolt. The buffer retainer spring is destroyed.

So I obtained a new Wolf Buffer spring, new retainer pin and spring, new buffer, and new bufffer tube from Brownells.
I tested the rifle and cycled the Bolt several times, and there was no problem. The Buffer retainer pin held its position under the edge of the Buffer tube which was thoroughly screwed in tight.

So at the range today, the same thing happened after about 5 rounds. The buffer retainer pin popped out, the buffer pin retainer spring was jammed under the BCA.
My loads are really not hot. Using Lapua Brass, 27.2 Gr of VV N140 and 123 gr 6.5mm Laupa bullet, and CCI primers.

What is with the Buffer system and how do I fix it? hve gone through 2 sets of parts...Is it the BCA?

Thanks. I know there is an expert here who can help out.

 

[RADcustom]

Re: Buffer Retaininer Pin and Spring Problem

A good picture of the problem area would help tremendously.

I suspect the tube.

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

I installed a brand new tube from Brownells.

 

[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

Is the buffer showing marks on the fwd face where it has struck the buffer ret pin during operation? When the upper assembly hinges down onto the lower receiver, the BCG SHOULD push the buffer back slightly and take the buffer spring tension OFF of the retaining pin. In other words, the buffer should not touch the retaining pin when the gun is fully assembled.

If the buffer has marks on its face where it strikes the pin every time the bolt slams home, the upper or lower receivers may be slightly out of spec. I HAVE A CURE FOR THIS and you won't have to replace any major parts or spend a lot of money doing it.

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

There were lots of marks on the Buffer edge that I changed out for anew one. Buffer was contacting the Buffer retainer pin.

What is the "CURE FOR THIS?"

 

[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

HOPEfully the buffer hitting the pin has not wallered the hole out in your lower receiver...

But any way, find somebody with a lathe and make a cut around the circumference of the buffer face about .125" (1/8") deep and about .030" longitudinally with the buffer. You are cutting a "step down" around the outside of the face of your buffer 1/8" wide and .030" deep below the level of the face. This allows the buffer face to extend OVER the retaining pin and still leavs plenty of original face area for the bolt carrier to push against.

I haven't been able to post pics but I may be able to figure it out if need be. It's very simple. You are providing a relief in the face of the buffer to allow the buffer to move thirty thousandths of an inch further forward before it hits the retaining pin. When the gun is closed up and the rear pin pushed in, the bolt carrier pushes back on the buffer and unloads the retaining pin like it's supposed to. This will allow the gun to function without striking the retaining pin.

I will add that the retaining pin is a mere convenience which keeps the buffer and spring captured when you break the gun down. It is not required for the gun to function normally, you just have to be careful when breaking it down.

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

Checked the bolt carrier and the channel is smooth and cleanly cut
The upper closes on the lower assembly and as is should slightly pushes the buffer back so it does not rest on the buffer retaining pin.
I have tried two buffer retainer pins one old and the other from Brownells that I put in this week.

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

MTFMN

Maybe I shoud try shooting without the buffer retainer pin and its spring...??

 

[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

Sure, just remember it ain't in there when you tear it down.

Even though the carrier pushes the buffer back slightly, it must not be enough or you wouldn't have marks on your buffer......

 

[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fx77</div><div class="ubbcode-body">Shooting an Alex Arms Upper in 6.5 Grendel
and a Bushmaster Lower. After about 5 rounds- all of which feed fine, the BCA jams. After opening the rifle the Buffer retainer pin and its spring are found under the bolt. The buffer retainer spring is destroyed.

So I obtained a new Wolf Buffer spring, new retainer pin and spring, new buffer, and new bufffer tube from Brownells.
I tested the rifle and cycled the Bolt several times, and there was no problem. <span style="color: #FF0000">The Buffer retainer pin held its position under the edge of the Buffer tube which was thoroughly screwed in tight.</span>

So at the range today, the same thing happened after about 5 rounds. The buffer retainer pin popped out, the buffer pin retainer spring was jammed under the BCA.
My loads are really not hot. Using Lapua Brass, 27.2 Gr of VV N140 and 123 gr 6.5mm Laupa bullet, and CCI primers.

What is with the Buffer system and how do I fix it? hve gone through 2 sets of parts...Is it the BCA?

Thanks. I know there is an expert here who can help out. </div></div>

I know you checked this, but are you sure you can't make another round with the buffer tube?

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

Checked the tupe twice. It is a new tube as well just received this wk from Brownells.

 

[srt_1]

Re: Buffer Retaininer Pin and Spring Problem

I'd like to know a cure for the as well... I have a surplus ammo & arms in 5.56 doing the same thing. Can ususally get 5 to 7 shots off before the pin and spring are both out and spring is destroyed. There is a mark on the buffer face where it strikes the pin. Just replaced the pin and spring from Brownell's. Would like to try and fix the problem before shooting again.

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

I replaced the pin,its spring, the tube, the buffer. and a new Wolff buffer spring...still happened.

 

[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mtrmn</div><div class="ubbcode-body">HOPEfully the buffer hitting the pin has not wallered the hole out in your lower receiver...

But any way, find somebody with a lathe and make a cut around the circumference of the buffer face about .125" (1/8") deep and about .030" longitudinally with the buffer. You are cutting a "step down" around the outside of the face of your buffer 1/8" wide and .030" deep below the level of the face. This allows the buffer face to extend OVER the retaining pin and still leavs plenty of original face area for the bolt carrier to push against.

I haven't been able to post pics but I may be able to figure it out if need be. It's very simple. You are providing a relief in the face of the buffer to allow the buffer to move thirty thousandths of an inch further forward before it hits the retaining pin. When the gun is closed up and the rear pin pushed in, the bolt carrier pushes back on the buffer and unloads the retaining pin like it's supposed to. This will allow the gun to function without striking the retaining pin.

</div></div>

^^THIS is the cure, although you'll never see this advocated by any self-respecting milspec worshipper. I'm sorry if it's hard to understand--I'll try to figure out posting pics if I can. Or better yet-PM me with an email address and I'll just email you the pics if you need them.

 

[trooper71]

Re: Buffer Retaininer Pin and Spring Problem

You've replaced everything and it's still happening. Just a thought, It could be the lower. If the buffer retaining pin hole is over sized, it might allow the pin and spring to be nudged out after being struck by the bolt carrier. I would take the lower off the upper and manipulate the retaining pin by hand. push it down and let it come up under its own pressure. Do this repeatedly and as fast as you can. Just a thought.

Good luck

 

[Hellbender]

Re: Buffer Retaininer Pin and Spring Problem

Your upper receiver is probably out of spec.

Is it a gun you may have to trust with your life or a toy?

If the latter.....then jerry rigging it with the buffer cut may work.

If the former, then take it to someone who can properly diagnose the problem.

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

Hellbender..life does not depend on it..

I may just shoot it withour the buffer retainer pin and buffer retainer spring..WTF?

 

[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

Maybe these pics will come out if I figured out how to do it.
I must add that this fix will stop the retainer pin from being hit by the buffer. It will NOT stop the retainer pin from coming out of it's bore if it is prone to doing this.

 

[2156SMK]

Re: Buffer Retaininer Pin and Spring Problem

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fx77</div><div class="ubbcode-body">The Buffer retainer pin held its position under the edge of the Buffer tube which was thoroughly screwed in tight.</div></div>

Assuming you are talking about an A2 buffer tube which has a shoulder that stops against the receiver, then your receiver is out of spec as the buffer retainer hole is too far forward.
Have someone with a lathe face off about 0.025" or so of the shoulder on the buffer tube.
That will allow the buffer tube to screw in more and properly retain your buffer detent.

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

Very good advice so far Thanks.
My eyes ain't what they used to be..neither is anything else, but another time

Under 3.5 X loupe magnification I note the hole in which the buffer ret. pin sits is not round. it is ovoid in the front and round in the back ..maybe from the pin slamming the front when the buffer retainer or the bolt catches it on the forward return?
Anyway than might explain how it could be levered out of its socket. May have to build another lower with a better buffer retainer pin hole or perhaps shim the buffer spring at the stock end limiting its excursion by an 1/8" or so???

 

[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

The buffer is obviously what's hitting the retainer or it would not have marks around the edge of the buffer face.

The fix shown in the pics I linked to WILL stop the buffer from ever hitting the retainer during operation. I had 3 ARs doing this-2 Deltons and 1 Blackthorne. I could swap uppers with a known good gun and the problem would go away--so the problem was NOT in my Superior Arms lowers. After some study and experimentation, I came up with the fix for the buffers. NONE of my retainers ever came out of the bore, I didn't shoot them enough to beat the hole out-of-round before I found the problem.

I'm sure the buffer tube could be modified similar to what 2156SMK said to do to the A2 buffer tube. The end could be ground down with notch for the buffer retainer. Then you could make an additional turn in on the buffer tube, with the notch lined up with the buffer retainer. This would definitely keep the retainer in it's hole, just have to worry about maybe the buffer or spring bottoming out in the tube. (I don't think they are so close to bottoming that 1 thread will cause a problem) You have extra take-off parts to work with, so you wouldn't be out much if it doesn't work.

I'm just going over what <span style="color: #FF0000">I</span> would do, I'm a life-long mechanic and I'm not afraid to do just about any kind of work on my own guns. Neither my life nor my livelihood depend on any of my guns. And since I named Blackthorne as 1 of the problem guns, you now know the quality of parts I learned on. I ran into a lot of problems I never would have had to figure out if I'd bought quality over quantity. Your mileage may vary.

ETA: Sorry, but shimming the buffer spring will accomplish nothing.

 

[MarinePMI]

Re: Buffer Retaininer Pin and Spring Problem

Looks like you put it in a rotary table and then milled the edge down, correct?

 

[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

That would work as well, but I just stuck it in a lathe. I brought the cutting tool to the face of the buffer and then indexed it toward the center of the buffer actually a little less than the 1/8" I stated before. About .120". Then I just cut .030" deep into the face of the buffer.

This cut leaves plenty of surface in the center of the buffer face for the bolt carrier to push against, and provides a relief for the buffer retainer so there will be no more collisions during normal operation. The buffer retainer does it's normal job of keeping the buffer contained when you break the gun down.

My <span style="color: #FF0000">FIRST</span> solution to the problem was to add a bit of metal to the rear of the bolt carrier.

I welded a bead on the rear of one of my bolt carriers with a 7018 rod, and worked it down until my carrier length was .030" more than original. This worked just as well, but is butt ugly and not recommended. That carrier is still in flawless operation and does it's intended purpose. <span style="color: #FF0000">DON'T try this one at home</span>. The buffer cut is much better and accomplishes the desired result much easier.

I'm sure there are a lot of ARs out there with this problem, but people don't know where the marks on their buffer come from. When they ask about it then all the big-name fanboys jump out there and pronounce the weapon a "cheap out-of-spec POS" and tell the poor hapless victim to go buy brand X or get another lower receiver which is essentially buying another gun anyway. I said eff that and proceeded to find a workable poor man's solution.

I found (in my case) through experimentation that it was the uppers that were most likely out of spec (I'm assuming) due to takedown/pivot pin hole location or maybe just too big. Put another upper on and it worked fine. Things only have to be off a few thousandths here and there and through "tolerance stacking" the gun is out of spec, causing this problem. It's all in the assembled relationship between the upper and lower receiver.

Now if the problem has caused the retainer to beat the bore out-of-round enough that the retainer can come out of it's own accord, then I would think maybe staking the fwd side of the retainer bore with a punch would displace metal into the void and provide expedient repair. As long as the modification is made to the buffer and the buffer is no longer hitting the retainer it should serve the purpose.

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

here is what the lower looks like with the buffer retainer pin and its screw removed. The buffer tube is fully screwed in.

URL=http://imageshack.us/photo/my-images/217/004sfu.jpg/]

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[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

Is this a collapsible stock or a fixed stock? It LOOKS like a fixed stock tube with the stock removed. If so, then the fix put forth by 2156SMK will work nicely to keep the buffer retainer in place.

As for the buffer modification, I been thinking all along it was a collapsible stock with a carbine buffer which I have a lot of experience with fixing. I haven't had to fix anything on my Colt which is the only fixed stock I own, so I'd have to go physically look at the rifle buffer to make sure the mod would still work.

From looking at your pic, CAREFULLY displacing some metal into the front side of that hole with a punch should keep the retainer from coming out. IF you were to do this, I suggest doing it with the retainer and spring IN PLACE. <span style="color: #FF0000">You must consider that this action will be a 1-shot 1-kill deal. If you screw it up, you just as well get another lower receiver.</span>

If your tube has a shoulder that butts against the receiver, then then cutting that shoulder back would be the way to go. Then the tube could be screwed in further like 2156 said in his post. If you read his profile, it says GUNSMITH

on there whereas I'm just a 1-tooth redneck shadetree mechanic.

Displacing metal with a punch should be a last resort in any case. Whatever you do, if anything, you must eliminate the buffer hitting the retainer first.

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

Fixed stock yes
Buffer tube has a shoulder yes

 

[mtrmn]

Re: Buffer Retaininer Pin and Spring Problem

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fx77</div><div class="ubbcode-body">Fixed stock yes
Buffer tube has a shoulder yes </div></div>

2156SMK has the fix for the tube, and my buffer modification will work with the rifle buffer as well as the carbine buffer. I just got back from my shop, where I went to look at my Colt to make sure about the buffer. You just need to find somebody with a lathe, and print this thread to take with you as well.

 

[Hellbender]

Re: Buffer Retaininer Pin and Spring Problem

fx77....
Per your pm:

It's impossible to diagnose without measuring and looking at the parts.
It's PROBABLY the upper receiver out of spec (most common) but could also be the lower, the bolt carrier, or even the barrel extension.
The pin and hole are only the symptoms of the bigger problem you are seeing.

I won't give advise on jerry rigging anything, I've seen too many people get shafted on "gun show specials", and had to fix too many of them.

Just shoot it without the the pin and spring if you want; it, in itself, won't hurt a thing. I have no idea if the true reason for the problem will get worse.

Always wear safety glasses when shooting any firearm!!

 

[fx77]

Re: Buffer Retaininer Pin and Spring Problem

FWIW ...shoots just fine without the buffer pin and spring...