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bigedp51
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Posted: 7/25/2012 12:42:53 PM
[Last Edit: 7/25/2012 1:55:36 PM by bigedp51]
I have a DPMS A2 HBAR and the base of the cartridge cases are scored and shave brass during ejection. It appears that the bolt is moving while the case is still under pressure and the bolt is shaving brass from the rear of the case. I reload and would like this damage to stop, what should be done to stop this.

Below is the type damage that is occurring to the cases, the ejector button and the lip of the bolt face under the extractor are shaving brass. I have seen two answers to this problem, 1. the extractor has too much spring force, 2. change the buffer. Are the extractor and buffer related to this same problem and would a different buffer slow down bolt rotation? If so is it a spring issue or the weight of the buffer or both.

NOTE: The damaged cartridge cases are brand new M193 ammo and not reloads.


Obo2
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Posted: 7/25/2012 12:59:19 PM
if these are your reloads they are too hot for that rifle.

When i do a load work up and see marks like that i know to back my load off at least a half grain or so.

bigedp51
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Posted: 7/25/2012 1:02:49 PM
[Last Edit: 7/25/2012 1:05:36 PM by bigedp51]
I just thought of this and edited my first post, they are not reloads and are brand new LC M193 mil-spec ammo. I do not plan to reload until this damage stops, I have brass OCD and this bothers me.
Krylancelo
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Posted: 7/25/2012 1:11:06 PM
I'd try a heavier buffer and see if that helps. If it doesn't, get a stronger action spring also. Check the extractor for any burs that may be digging into the brass.
Obo2
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Posted: 7/25/2012 1:13:45 PM
is that a factory new pmc too?
Krylancelo
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Posted: 7/25/2012 1:18:09 PM
Here's a question, what happens if you cycle the gun by hand? Does it still have marks?
bigedp51
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Posted: 7/25/2012 1:49:29 PM
[Last Edit: 7/25/2012 1:51:06 PM by bigedp51]
It does not leave any marks on the case when cycled by hand.

This same question was asked at M4Carbine.net and NO definitive answer was given or simply put MANY answers were given from the extractor, buffer to one of the big boys saying he had a non mil-spec gas port and should have bought a Colt. I'm retired and trying to save money and fix the problem in one shot and I believe I have two more buffer weights to choose from.

My son has a 16 inch S&W M&P 15T carbine and I was thinking about swapping buffers, BUT how can you tell the weight of the buffer and which weight buffer would stop the problem. And last does the weight of the buffer actually slow down bolt rotation enough to stop this problem or could over gassing be the problem. I have a 20 inch barrel with what I assume is a rifle type buffer and gas system, meaning gas port diameter and dwell time.

Forgive me for asking these questions but my bolt actions are operated by calories and rotational force expended.
rob78
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Posted: 7/25/2012 1:56:34 PM
[Last Edit: 7/25/2012 2:06:37 PM by rob78]
A heavier buffer will slow the BCG.

That's a strange place to get those marks and I can see why a heavier buffer was recommended. The bolt is slamming into the case when feeding from the magazine hard enough to gouge the brass.

IMO, a heavier buffer would be my first fix.


If that doesn't work, it may be time to try a new recoil spring. Don't do this until you've tried a heavier buffer. We don't want to introduce too many variables.

ETA2: Just saw your edit. I don't know that a heavier buffer will slow the bolt unlocking that much. Are you sure your rifle is chambered 5.56 and not 223?
ETA: Photos of different types of buffers to help you with identification.

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bigedp51
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Posted: 7/25/2012 2:09:03 PM
Originally Posted By Obo2:
is that a factory new pmc too?


Obo2

I threw my damaged brass away and did not take any photos of it, the posted photo came from that "other" AR website and shows the exact same type damage I'm having and that is why I posted this photo. As soon as I saw "MY" damaged brass LC M193 cases I switched to steel case ammo to do no further damage to this factory loaded ammunition.

I have a full five gallon bucket of once fired Remington .223 brass ready to load but I'm not going to shoot this prepped brass if the AR is going to eat the cases.

bigedp51
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Posted: 7/25/2012 2:22:43 PM
[Last Edit: 7/25/2012 2:38:31 PM by bigedp51]
Originally Posted By rob78:
A heavier buffer will slow the BCG.

That's a strange place to get those marks and I can see why a heavier buffer was recommended. The bolt is slamming into the case when feeding from the magazine hard enough to gouge the brass.

IMO, a heavier buffer would be my first fix.


If that doesn't work, it may be time to try a new recoil spring. Don't do this until you've tried a heavier buffer. We don't want to introduce too many variables.

ETA2: Just saw your edit. I don't know that a heavier buffer will slow the bolt unlocking that much. Are you sure your rifle is chambered 5.56 and not 223?
ETA: Photos of different types of buffers to help you with identification.

http://www.ar15barrels.com/tech/buffer-construction.jpg


Now I'm really confused, a heavier buffer and spring will cause the bolt to slam home that much harder and do even MORE damage if what you say about the damage being caused on bolt closing. Also I would have to have the headspace set too tight to do this type damage on bolt closing due to having no head clearance behind the case.

Forgive me but damage due to early bolt opening seems more plausible, BUT I'm not an expert so don't take this wrong way.

Also the rifle buffer appears to be the heaviest of all the buffers so this leaves spring weights to possibly solve the problem. Which asks the question, has anyone had this problem with damage brass and did you fix the problem.

And it is chambered in 5.56

Krylancelo
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Posted: 7/25/2012 2:32:22 PM

Originally Posted By bigedp51:
Originally Posted By rob78:
A heavier buffer will slow the BCG.

That's a strange place to get those marks and I can see why a heavier buffer was recommended. The bolt is slamming into the case when feeding from the magazine hard enough to gouge the brass.

IMO, a heavier buffer would be my first fix.


If that doesn't work, it may be time to try a new recoil spring. Don't do this until you've tried a heavier buffer. We don't want to introduce too many variables.

ETA2: Just saw your edit. I don't know that a heavier buffer will slow the bolt unlocking that much. Are you sure your rifle is chambered 5.56 and not 223?
ETA: Photos of different types of buffers to help you with identification.

http://www.ar15barrels.com/tech/buffer-construction.jpg


Now I'm really confused, a heavier buffer and spring will cause the bolt to slam home that much harder and do even MORE damage if what you say about the damage being caused on bolt closing. Also I would have to have the headspace set too tight to do this type damage on bolt closing due to having no head clearance behind the case.

Forgive me but damage due to early bolt opening seems more plausible, BUT I'm not an expert so don't take this wrong way.

And it is chambered in 5.56


I highly doubt damage is being caused on bolt closing. Because if it were, you hand cycling it would have very close to the same velocity (it's only the return spring and buffer even when actually fired unless it's actually bouncing off the back of the receiver extension which says to me way over-gassed), and would also be causing the problem.

Are there any over-pressure signs on the casings?
bigedp51
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Posted: 7/25/2012 2:41:24 PM
[Last Edit: 7/25/2012 2:52:04 PM by bigedp51]
Originally Posted By Krylancelo:

Are there any over-pressure signs on the casings?


NO, I inspected the cases and I have been reloading for over 45 years.

There are no sharp edges on the bolt face or at the ejector button.

Below is the ammo in question, has anyone heard about any problems with this ammo or if Federal changed to a slower burning powder or upped the pressure?



Obo2
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Posted: 7/25/2012 2:47:45 PM
those swipes are over pressure signs.

I'd load up a ladder test of your own reloads I bet you won't get it if you actually load in sammi spec instead of those factory 556 loads
bigedp51
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Posted: 7/25/2012 2:56:27 PM
Originally Posted By Obo2:
those swipes are over pressure signs.

I'd load up a ladder test of your own reloads I bet you won't get it if you actually load in sammi spec instead of those factory 556 loads


You are correct, BUT that wont fix the problem with the existing ammo. I have a 5.56 throat and I'm shooting mil-spec ammo and down loading the ammo doesn't fix the problem.

rob78
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Posted: 7/25/2012 3:23:23 PM
Originally Posted By bigedp51:
Originally Posted By rob78:
A heavier buffer will slow the BCG.

That's a strange place to get those marks and I can see why a heavier buffer was recommended. The bolt is slamming into the case when feeding from the magazine hard enough to gouge the brass.

IMO, a heavier buffer would be my first fix.


If that doesn't work, it may be time to try a new recoil spring. Don't do this until you've tried a heavier buffer. We don't want to introduce too many variables.

ETA2: Just saw your edit. I don't know that a heavier buffer will slow the bolt unlocking that much. Are you sure your rifle is chambered 5.56 and not 223?
ETA: Photos of different types of buffers to help you with identification.

http://www.ar15barrels.com/tech/buffer-construction.jpg


Now I'm really confused, a heavier buffer and spring will cause the bolt to slam home that much harder and do even MORE damage if what you say about the damage being caused on bolt closing. Also I would have to have the headspace set too tight to do this type damage on bolt closing due to having no head clearance behind the case.

Forgive me but damage due to early bolt opening seems more plausible, BUT I'm not an expert so don't take this wrong way.

Also the rifle buffer appears to be the heaviest of all the buffers so this leaves spring weights to possibly solve the problem. Which asks the question, has anyone had this problem with damage brass and did you fix the problem.

And it is chambered in 5.56



A heavier buffer reduces BCG velocity.

But I think you're correct that this may not be a BCG velocity issue.

The pic I posted was just to ensure that you were, in fact, using a rifle buffer.

5.56 chamber in your rifle? there goes my other theory.
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Obo2
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Posted: 7/25/2012 3:25:24 PM
right won't fix that ammo but you can see if you have to worry about chewing up your brass that you loaded.

The others gave some good suggestions so far for the current ammo.

Basically the fix is to slow down the bolt unlock whether that be a heavier buffer or spring, an adjustable gas block or beavers.
rob78
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Posted: 7/25/2012 3:26:58 PM
Originally Posted By bigedp51:
Originally Posted By Obo2:
those swipes are over pressure signs.

I'd load up a ladder test of your own reloads I bet you won't get it if you actually load in sammi spec instead of those factory 556 loads


You are correct, BUT that wont fix the problem with the existing ammo. I have a 5.56 throat and I'm shooting mil-spec ammo and down loading the ammo doesn't fix the problem.



Have you tried other lots/types of 5.56 ammo?

Same signs?

Does your rifle do this with 223 ammo?


As to your earlier question, I have had issues with XM193. Black box American Eagle. Hard primers and a few ejection issues. I chalked it up to inconsistent ammo production since the rifle ate everything else.
"A goverment that's big enough to do everything for us, is powerful enough to do anything to us."
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Krylancelo
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Posted: 7/25/2012 3:27:49 PM
I would check your chamber size with a 5.56 reamer if you have it. There have been reports of undersized 5.56 chambers coming out lately that are undersized and that would cause overpressure problems (like shooting 5.56 in a .223 chamber).
bigedp51
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Posted: 7/25/2012 3:29:45 PM
In the past Lake City was given waivers to raise the chamber pressure to 60,000 cup from the standard 52,000 cup rated chamber pressure with M193 ammo to meet the required velocities with different lots of powders. The .223 and "NORMAL" M193 military ammunition are rated at the same chamber pressure with the only difference being the throat in these two cartridges.

The brass is not flowing into the ejector hole in the bolt face and thus indicating higher than normal pressures. I have a bolt action .223 and this AR and I have shot M193 ammunition in this bolt action without any pressure signs. The civilian firearms industry is now manufacturing .223 rifles with longer throats and my .223 is one of them.

It could be possible that my AR is causing the problem, BUT shooting the lower pressure steel case ammo has the same type marks on the rear of the cases. I think the problem is caused by early opening of the bolt but this is just guesswork.
bigedp51
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Posted: 7/25/2012 4:10:04 PM
[Last Edit: 7/25/2012 4:17:23 PM by bigedp51]
I just weighed the rifle buffer assembly without taking it apart and it weighs 8.5750 ounces. Is that weight equal to the total of both weights given in the chart above?

I also just weighed my PSA lower kit buffer and unassembled it weighed 8.6950
rob78
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Posted: 7/25/2012 4:16:29 PM
Originally Posted By bigedp51:
In the past Lake City was given waivers to raise the chamber pressure to 60,000 cup from the standard 52,000 cup rated chamber pressure with M193 ammo to meet the required velocities with different lots of powders. The .223 and "NORMAL" M193 military ammunition are rated at the same chamber pressure with the only difference being the throat in these two cartridges.

The brass is not flowing into the ejector hole in the bolt face and thus indicating higher than normal pressures. I have a bolt action .223 and this AR and I have shot M193 ammunition in this bolt action without any pressure signs. The civilian firearms industry is now manufacturing .223 rifles with longer throats and my .223 is one of them.

It could be possible that my AR is causing the problem, BUT shooting the lower pressure steel case ammo has the same type marks on the rear of the cases. I think the problem is caused by early opening of the bolt but this is just guesswork.


Most folks here are aware of the differences in chambering. I was not aware that 223 chambered rifles were being reamed with a mil-spec leade dimension.

You can see overpressure signs in a SAAMI-chambered rife if firing 5.56 ammo. Similar cpu, different chamber dimensions, can lead to excessive pressure. Please note the qualifier "can". I don't need to tell you that your bolt rifle's performance has no bearing on how your AR may handle this. But this is irrelevent since you've stated that the barrel is stamped 5.56.

Not insulting your intelligence here, but need answers to basic questions:

1) Clean chamber? If you're shooting steel case ammo, you get excessive residue in the chamber walls since the steel will not expand to fill the chamber. Most of the time, switching to brass without a decent cleaning leads to stuck cases. Have enough buildup and it could create high pressure signs.

2) Have you modified this rifle in any way? Changed out gas block, gastube, anything?

3) How long have you been shooting this rifle? Subsequently, When did you notice this issue? Happening all the time or did it just start occuring out of the blue?

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rob78
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Posted: 7/25/2012 4:25:10 PM
Originally Posted By bigedp51:
I just weighed the rifle buffer assembly without taking it apart and it weighs 8.5750 ounces. Is that weight equal to the total of both weights given in the chart above?

I also just weighed my PSA lower kit buffer and unassembled it weighed 8.6950



Ain't no way. You're not weighing them correctly. Rifle buffer should weigh a hair over 5ounces.

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j3_
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Posted: 7/25/2012 5:55:10 PM
[Last Edit: 7/25/2012 5:59:19 PM by j3_]
May just be burrs on the bolt face at the ejector and extractor. You can usually find them by sliding something like a small jewelers screwdriver across the bolt face and feel where it hangs up on at the edge of the extractor cut out and ejector hole.
Make sure the bottom of the groove in the extractor lines up correctly/evenly with the bolt face.
Swap bolts and see it it quits.
Obo2
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Posted: 7/25/2012 6:01:18 PM
[Last Edit: 7/25/2012 6:59:07 PM by Obo2]
removed I'm dumb
rob78
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Posted: 7/25/2012 6:43:54 PM
Originally Posted By Obo2:
Originally Posted By rob78:
Originally Posted By bigedp51:
I just weighed the rifle buffer assembly without taking it apart and it weighs 8.5750 ounces. Is that weight equal to the total of both weights given in the chart above?

I also just weighed my PSA lower kit buffer and unassembled it weighed 8.6950



Ain't no way. You're not weighing them correctly. Rifle buffer should weigh a hair over 5ounces.



well the chart above shows reciprocal weight (Just the weights that move inside)

I never weighed my buffer or it's weights i just know its a stock car but thought i should point out that little note on the chart


it also lists overall weight. IIRC, a std. rifle buffer weighs 5.2oz
"A goverment that's big enough to do everything for us, is powerful enough to do anything to us."
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bigedp51
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Posted: 7/25/2012 10:27:27 PM
I just calibrated and double checked my electronic scales, I'm getting the correct weight for the calibration weight and checking 55 grain bullets BUT a 500 grain bullet indicates a minus (-687.3 grains) so it it is having a nervous breakdown with heavy objects. My balance beam scales will not weigh anything over 500 grains so I have nothing to accurately weigh the buffers.

20 gram calibration weight



55 grain bullet



Rifle buffer set on ounces

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