AR-15 buffer. Metal erosion?

[coloradokevin]

Well, I'm kind of stumped on this one...

I was looking at my two AR-15's side by side tonight.

The first rifle is a Bushmaster that I personally own, and the other rifle is a Colt AR-15 that my department issued to me.

Anyway, I noticed that the buffer on MY rifle appears to have some evidence of metal erosion. The area around the outside of the bufer (where the bolt carrier contacts it) shows a rough ring where it looks like some material has been scoured away). Additionally, the back of the bolt carrier on this rifle appears silvery in color, similar to the color of the bufer assembly... When I run my finger over the back of the bolt carrier, I pick up some shiny/silvery residue on my fingers.

By comparison, I have no such marks on the bufer of my dept-issued Colt rifle, nor do I have any similar looking residue on the back of the bolt carrier.

I've owned my Bushmaster for a number of years, and the Colt rifle was new less than two years ago. Regardless, I've probably shot the Colt significantly more than my Bushmaster, given that ammo at work is free.

I'm a bit disturbed by this problem, as I can't seem to figure out what is wrong with my rifle that would cause some friction (?) between the bolt carrier and the bufer assembly?

Anyone have any thoughts on this issue?





In case my explanation was not clear, here are some pictures of the parts from these two different rifles:


The Colt without the problem:








The Bushmaster I'm concerned about:

 

[nicholst55]

Perfectly normal. You do realize that the bolt carrier slams into the face of the buffer, each and every time you fire the rifle, right? That's what causes this condition, and it doesn't hurt a thing.

 

[taliv]

can't see the pics

 

[PTK]

Odd, my DSA AR15 with many thousand rounds through it looks closer to your Colt than your Bushmaster in regards to the buffer and BC.

 

[TexasRifleman]

I have a Bushmaster with well over 10,000 rounds through it and it doesn't show anything like what is seen here.

What the picture doesn't show is the depth of the eroded/worn ring area on the buffer.

Can you actually feel the difference with your finger or measure it?

Or is this just something visual?

 

[RyanM]

Well, I notice the Colt has an H buffer. Materials for H buffers depend on the manufacturer. Maybe that one's made of steel. Normally they're aluminum, and the H buffers just have weights in them, but Colt does a lot of weird things to their ARs.

Try poking it with a magnet.

 

[taliv]

but Colt does a lot of weird things to their ARs.

you mean like build them to a spec?

 

[Zak Smith]

It can also be due to the buffer hitting the buffer retaining detent all the time. This can cause eventual failure of the detent, in which case its broken parts might migrate into the FCG or bolt and cause a failure. I have seen that happen.

 

[rcmodel]

A dab of Grease might help!

rcmodel

 

[shoestring]

Perfectly normal. You do realize that the bolt carrier slams into the face of the buffer, each and every time you fire the rifle, right? That's what cuases this cindition, and it doesn't hurt a thing.

Here is your answer. I also have a Bushmaster and it shows some wear but with frequent cleaning it wont hurt a thing. Some of the Bushmaster parts are a little on the cheap side.

 

[TexasRifleman]

A dab of Grease might help!

I have never seen anyone lube that part of the rifle.

You put grease there on yours?

 

[rcmodel]

I put a dab of grease on anything that has two pieces of dry metal slamming and rubbing on each other!

If it wears the finish off, it's a friction point, and should be lubed.

rcmodel

 

[coloradokevin]

Thanks for the replies everyone!

I realize that these are full-contact parts within the gun. But, my concern came up when I realized that the Colt doesn't show this issue, and the Bushmaster does!

Again, the Colt is a much newer rifle, but has had more ammunition through it (to the tune of many thousands of rounds).

I also wondered if perhaps the two buffer assemblies were made out of different materials. I'll take another look at them here in a minute, and report back with my findings!

 

[Coronach]

I agree that the problem is almost certainly the BC hitting the buffer and etching the surface of the buffer. The marks seem to match up perfectly with the rear of the BC.

However, I have never seen marks like THAT, though my experience is more limited than Zak's and Taliv's. My RRA has a whole lot of rounds through it, and the buffer looks like the Colt buffer. Something doesn't seem right with the Bushmaster.

Did you do a BC upgrade of some sort? Perhaps some super-hardened surface finish? What about the buffer? Is that a standard buffer?

Mike

 

[TexasRifleman]

I put a dab of grease on anything that has two pieces of dry metal slamming and rubbing on each other!

If it wears the finish off, it's a friction point, and should be lubed.

Well just FYI no M16 or AR maintenance guide shows that to be a place for grease so just keep that in mind. Extra grease and the AR/M16 platform don't go well together.

I would not put grease there. The buffer is intentionally made of a softer metal than the bolt carrier and is "sacrificial".

 

[Bartholomew Roberts]

I have a Bushmaster standard carbine buffer with about 12k rounds on it. While it shows some wear in the same areas and definitely doesn't look as nice as your Colt, it is nowhere near as bad as the Bushy buffer in your picture. It has also seen a thousand rounds or so suppressed, so it gets thumped pretty good.

I would check the buffer retaining pin for any indication that the buffer may be impacting there (should be corresponding finish wear if so). If not, then all I can guess is that not all parts are equal. It certainly wouldn't be the first time someone cut corners on an AR buffer.

 

[briansmithwins]

I suspect the the back of the Bushie bolt carrier has a burr on it. I also agree the it's possible the buffer is hitting its retaining pin.

BSW

 

[Frog48]

My Bushmaster doesnt look like that. Mine looks like the pic of the Colt.

 

[rcmodel]

Extra grease and the AR/M16 platform don't go well together.

AHhh!
I will have to keep that in mind.
Must be why my 1970 Colt AR has still yet to miss a beat in 38 years!

I bet it would be twice as reliable (200 percent?) if I hadn't kept a dab of grease & oil here & there where the manual didn't mention one.

It's been my experiance that far more AR problems can be traced to not enough lube, not too much!

rcmodel

 

[Onmilo]

In my experience, a bolt carrier that is on the minimum side of overall length tolerence will impact the bolt buffer while a bolt carrier that is on the maximum side of length tolerence will actually set against the buffer and will push it sightly back into the extension tube when the shooter closes the upper onto the lower receiver.
This longer carrier makes for smoother cycling and little or no markings on the buffer face.

The marking of the face of the buffer has absolutely no impact on the reliability of the weapon, it is a cosmetic issue only.

A big wad of grease on the buffer face will only mean a big wad of grease in the extension tube or shoved out into the fire control area.
Wads of grease pick up foreign material much more readily than a semi dry or lightly oiled area and foreign material will affect reliability as well as scratch surfaces causing more cosmetic issues.

There are buffer face pads on the market now made of the same material as the shock pad on the back of the bolt buffer if you just cannot stand marks on your buffer.

As some have noticed, certain companies produce parts with maximum dimensions in all the right places.
It is one of the reasons the parts they offer cost more than other vendor offerings.

 

[mp510]

The buffer in my AR looks just like your Bushmaster buffer with the ring in it from the carrier. I don't know who made my buffer (my rifle is a mix-master that I bought used), but my upper is a Bushmaster, and the rifle came with a Bushmaster mag, so the buffer too may be a Bushmaster (but I really don't know). That said, I don't consider it abnormal. Nor am I concerned. There is no damage to my carrier.

(The flash from my camera impedes on the picture quality)

 

[rcmodel]

A big wad of grease

Nobody said anything about a "big wad of grease"!

I said a dab, which is many froghairs smaller then a wad.

rcmodel

 

[Onmilo]

"Many froghairs smaller"
I stand corrected.
A small dab is a-ok

 

[Coronach]

You know, on second consideration, I bet the flash in the OP was doing the same thing as mp510's. I checked my RRA, and it does have some etching, and if you hit it with a flash from a camera, it might look something like that.

That still seems extreme, but it's probably nothing to worry about. Just a case of a soft surface being etched and eroded by a harder one.

Mike

 

[Don't Tread On Me]

Various possibilities.

A few years back I read of some Bushmaster lowers being out of spec. The buffer retaining pin hole is drilled just slightly too far back. This causes the buffer to hit the buffer retaining pin. As it rotates around, it can create that. Also, if it is hitting the buffer retaining pin - that means it is not mating up against the back of the carrier flush and with contact. So when the carrier comes recoiling back - instead of going with the buffer, it first slams into the buffer. Even if it's a few thousandths ...it can make a difference.

Think of it like this. Hold a rifle to your shoulder. Your shoulder moves with the recoil. Now hold that rifle 1/2" off your shoulder and you get smacked and it hurts.

The etching on that buffer face seems extreme. Now, since there is always contact ...yes, some marking does occur on all AR-15's. And if you have none, you eventually will as you shoot more rounds OR you have an extremely flush buffer face and bolt carrier rear.


Could also be materials playing a role too. My Colt has almost no marking, while my built AR with Bushmaster buttstock/buffer is showing marking. Although, not as extreme as that.


I don't know if yours is out of spec or not. But those past Bushmasters that were goes to show why Colt and FN are better. Their lowers are subjected to tests to ensure each one is in spec. I doubt Bushmaster runs them in those robotic machines. Then people wonder why a Colt lower is 2x the price.


Sorry about that, back on topic.


This is how you can test it. Open up the receivers. As you close the upper to the lower, view it from the side against a light or a bright background. Go slow. You should clearly see the back of the carrier engage the buffer and push it back as it comes down. Keep looking through the crack in the upper/lower as long as you can till it closes. That's because the buffer is always tilted forward at the top because it is being held in at the bottom. If that makes sense to you? So keep following it till you can see a hint of light at the bottom or enough movement back where you know it has disengaged from the buffer retaining pin.

Finally, there's different levels of this flaw. There's situations where the buffer retaining pin eats most of the buffer force causing it to make buffer pin sized dents in the buffer. This swells the edge of the buffer where those dents are, causing it to grind inside the buffer tube. That's about the worst case scenario and will eventually lead to breakage. All depends how many thousandths off the hole or pin is.