Help: dirty/damaged brass

[Bunk39]

I'm new to the AR-10 world. Shooting a JP Rifles PSC12 upper on a DPMS lower. Recently added a TBAC 30p-1. The rifle has 200+\- through it. No problems w the rifle running prior to adding the TBAC. However, the brass always has two small gouges in the neck after firing. Unfired, ejected rounds do not have this. Is this common for AR-10's?
Since adding the suppressor, my brass comes out filthy. Is that common for AR-10's? It's dirty to the point of failing to eject. Fouls my chamber in a hurry. Plenty of lube seems to solve the problem. But I hate to chance firing w lube in the barrel. I've got my gas turned down by more than half my unsuppressed setting on my block. Would adding another click or two of gas help?

Suggestions...comments?

Thanks


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[cajun 22]

Running a suppressor on any gun will dirty the brass and the gun because of the backpressure created by the can. Fact of suppressor life. As for the gouges in the neck, the brass is expanding a little more than unsuppressed and there is something in the chamber causing this. I have several hundred rounds through an AR10, suppressed, without any abnormality to the brass other than dirty. I adjust the gas down until it will not hold the bolt open on the last round and open it back up until it locks. That may take some pressure off of the chamber and your brass. Are there any marks on unsuppressed ejected rounds?

 

[Bunk39]

Yes there have always been marks on the brass from the beginning


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[ajridgedell]

some pictures of the marks would help us identify what it could be

 

[Golden Dragon]

JP LRP-07™ rifles chambered in 7.62x51 are designed to function with SAAMI spec. commercial-grade factory .308 Winchester ammunition. We recognize that many avid shooters reload for their rifles, and carefully assembled hand loads should function when appropriate component combinations are used and brass is properly sized and gauged. However, we will not warrantee damage caused by hand-loaded ammunition that is not compatible with the rifle.

We do not recommend the use of surplus military ammunition due to the considerable variation from manufacturer to manufacturer, lot to lot, year to year, and from the components used and the processes in manufacturing. In some cases, surplus ammo has been mass tumbled to clean the years of tarnish off the cases, which actually causes the powder to break down. This drastically changes the burn rate of the propellant and the subsequent internal ballistic characteristics of the load, leading to the potential for extreme pressures.

Much surplus ammunition is not made to exact specifications. We have found that some of this ammunition has caused problems in our rifles due to the use of a tar-like sealant for waterproofing. When this ammunition is used in our rifles, this sealant melts and coats the chamber causing failures to extract and to chamber. Afterwards, any rifle in which this ammunition is used will have the same problem if the chamber and the bore are not cleaned thoroughly. We have found that surplus ammunition from the following countries/manufactures will cause these problems in our rifles:

South African
Venezuela Cavim
Austrian Hirtenberger
Some lots of German
British (underpowered—will not cycle action)
Indian (overpowered)
Winchester white boxes marked 7.62
Wolf steel cased (fouls chamber with coating)


If you have used ammunition that causes chamber fouling leading to extraction failures, you must thoroughly clean the chamber and the bore before using any other ammunition. Then, try commercial .308 like Federal American Eagle 150gr. FMJ or Remington UMC 150gr. FMJ to function test the rifle.

LRP-07™ rifles chambered in .260 Remington

The LRP-07™ chambered in .260 Remington is designed primarily for the skilled hand loader, as there is little available in accurate factory .260 ammunition. Best accuracy is usually achieved at about 10% below recommended maximum load data in recognized loading manuals. Be aware that canister powders can vary significantly in burn rate from one lot to another and if you start a new lot of powder, it may be necessary to work up a new load. Do not assume that a *factory* load for the .260 will perform satisfactorily in your LRP-07™ and assume that there is something wrong with the rifle if a particular ammo fails to function or exhibits high pressure signs. Available factory ammunition is designed for rifles with 1:9 twist barrels. We use a 1:8 twist barrel for improved accuracy with certain high BC-type projectiles. This may not be compatible with some factory loads. You may experience high pressure failures such as dropped primers and excessive bolt velocity resulting in extraction/ejection failures or even possible ruptured cases. If high-pressure signs are evident with any ammunition, discontinue use of that ammunition immediately.

Remember that gas-operated semi-automatic rifles in any caliber are much more ammo sensitive than manually operated rifles. You must find or load ammo that is compatible with the rifle, not expect that the rifle can be made compatible with the particular ammunition that you have chosen.

****From JP website****

 

[Bunk39]

Here's a picture of three cases w damage. It's a little hard to see. You are looking at marks or 'scores' in the neck area. But it's not the same every time. You can see that in the case on the left. It only has one mark and almost looks like the case "bumped along" as it was ejected. Could this be the cases hitting the lugs on the barrel extension as it ejects?

I have used one ammo listed on the excerpt from the JP website. The Winchester white box of 7.62.
The other ammo I'm shooting is Lake City 175 gr Sierra OTM and Uncle Ted w 180 grain Barnes TTSX. They both group very well in my rifle.

While that JP info is helpful, I don't have a JP barrel. It's a Bartlein that was chambered by a person they recommended. Craddock precision.

Anybody have a bore scope?

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[ajridgedell]

I would say its not normal. if it did it from day one, maybe a bur or something in the neck of the chamber. If it were my rifle, I would try to make certain that those burs are coming from the chamber, then wrap a patch with jb bore past on a brush and spin it with drill in the neck of the chamber. best bet would be to look at it with a borescope to be certain thats the problem though.

 

[Judge Mental]

When I purchase my M&P10, I bought 2 boxes of .308 ammo recommended by the salesman. FTE's on every other round, with the cases stuck in chamber and requiring squib. Returned the gun to my LGS, and the gunsmith polished the chamber. When returning the gun, he asked what ammo I was using. I showed him on the shelf the cartridges, and he said, "There's your problem. Those are made for FAL and bolt action weapons, not the AR10 platform." They then made the unusual gesture of swapping the ammo, "our bad". Too much compression causing too much case expansion leading to FTE. Extractor actually pulled the lips off of one case.
When new, the feed ramps also grooved my case necks somewhat.

 

[Bunk39]

That's some good info. I have just spent some time partially inserting a spent case, then slowly ejecting it. The lines on the necks are definitely being made by the lugs or splines on the barrel extension that the bolt passes through to lock. I can rotate the case, and repeat the procedure and it draws two new perfect lines down the neck where it contacts two of the splines on its way out to be ejected.

As for the stuck spent cases, it only started doing that recently with the introduction of the suppressor into the equation. Seems like my Lake City 7.62x51 NATO is doing it a bit more. Can anyone shed any light this. Does the NATO run at a higher case pressure?

I'm leaning toward having a much dirtier gun due to the suppressor. Also, could the suppressor be increasing the pressure enough to cause greater expansion of the neck? This along with the dirty chamber could be causing the stuck cases?

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[ajridgedell]

One powder may burn dirtier than another powder causing even more fouling with the silencer. I've had a case get stuck in the chamber from shooting with a silencer then just leaving the last round chambered, when i came back and shot a few days later it was stuck. If fouling is causing your cases to get stuck either cleaning and trying to polish up the chamber may help, or trying some different rounds that burn cleaner. To my knowledge a silencer shouldn't increase pressure any. If over pressure is concern post a pic of the case head and we should see some pressure signs there.