is this something to be concerned about? (AR-15 related)


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MyRoad
September 9, 2008, 09:33 PM
I don't have a lot of experience with AR's, and now I find myself owning two, and learning to like them.

I was breaking in a new DPMS SS Match upper today, and I noticed this bit of 'fouling' just ahead of the gas block (?). Is that, "normal"? Big problem? Small problem? No problem?

Thanks -

http://www.xlr8nrg.com/images/ar_fouling.jpg

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EShell
September 9, 2008, 09:34 PM
Some leakage, like this, is normal.

gregormeister
September 9, 2008, 09:37 PM
If you'd ever seen my service rifle then you'd be relieved to know that your rifle is fine and dandy....I would say its no big problem....If it is affecting the finish then a AR-15 experienced gunsmith can probably help you along...

taliv
September 9, 2008, 09:40 PM
not normal

even so, not likely to be a big problem

MyRoad
September 9, 2008, 09:41 PM
Thanks for the quick replies. I'm not worried about the finish, and the gun shoots beautifully. I just wanted to be sure that gas escaping from an unintended location was not indicative of sloppy assembly, or some sort of problem that could become an issue over time. My initial assumption was that if I shoot it enough, the hole will eventually clog up... and therefore no longer be an issue.

brian923
September 9, 2008, 10:14 PM
if the hole cloggs up, eventually , it will work its way into the gas tube causing feeding and extraction problems. also, as hot gases escape out of the hole, at the velocitys they are traviling, it could cause it to burn (melt) a bigger hole in the FSB, or etch your barrel allowing it to rust. (might not, as i am not a certified gunsmith) i would contact DPMS and have them either look at it and install a new front sight base, or get them to send you a new one, and install it yourself. there should be no problesm as i have heard that dpms customer service is very reputable. brian

taliv
September 9, 2008, 11:16 PM
oh, it's indicative of sloppy assembly alright

FlyinBryan
September 9, 2008, 11:35 PM
i would send the same pic to dpms and hear what they had to say about it.

what could it hurt.

EShell
September 10, 2008, 07:23 AM
I've added to this collection since this picture below was taken, and, drawing from personal experience, I'd maintain that some leakage is normal. Not leaking is much farther from the norm.

The only one I've ever seen not show signs of gas leakage in this area is .835" JP gas block I had to hone to fit to a 24" Kreiger barrel, and that one leaked back around the gas tube entry bore. Production FSBs are not hand fitted or honed for a flawless fit.

Every one of these rifles, Armalites, Bushys, Colts and a few I put together myself, as well as several spare uppers I have, show some sign of gas leakage around the FSB. The SS barrel makes this example look more severe than it ordinarily would with a Parked finish.

Further, this example also looks more like a small amount of gas blew a large amount of (stained) oil out from under the FSB. Looking closely at the photo, it is very obviously a liquid stain, not just dry gas. The bore/gas port either contained an excess amount of oil or solvent, or the assembly/shipping oil was still present on and around the FSB in excess amounts. Just like a very small amount of blood can go a long way, I'd suggest that this oil makes it look much worse than it really is.

By all means, call DPMS, but don't think they're just blowing you off if they act like it's a non-problem, since I'd expect you to hear them tell you the same thing.

http://www.pillicustomhomes.com/eshell/213/AR15-herd1.jpg

taliv
September 10, 2008, 09:25 AM
eshell, can you post pics of signs of leakage on your guns?

TexasRifleman
September 10, 2008, 09:36 AM
The thing is that most people with standard finishes won't notice it anyway even if it's there. Only when you get a nice shiny barrel do you see it.

I bet there are lots more rifles that leak like this than people realize, you just can't see it easily unless the barrel is shiny.

I only have one "shiny barrel" upper and it shows a little of this, not as bad as the OP but a small amount.

As EShell says, that looks like oil from assembly. The gas leaking out may be a very small amount but it's blowing this oil out. I would expect that to go away after a short time.

EShell
September 10, 2008, 10:05 AM
eshell, can you post pics of signs of leakage on your guns?
Not easily. I just looked at my individual pics and don't have any now that are of sufficient resolution to see the FSB/Gas block areas. Most of my rifles are relatively clean now anyway, but I'll look at some tonight and see if I have any that show up well enough to take a picture of.

I'm working the Wounded Warrior shoot at Quantico this Saturday and will be letting the guys use a couple of my rifles, so I should be able to get something for you over the weekend.

I will say right now that none of mine are going to spray oil like that. . . any oil that may have ever been there is long burned off and/or blown away.
The thing is that most people with standard finishes won't notice it anyway even if it's there. Only when you get a nice shiny barrel do you see it.

I bet there are lots more rifles that leak like this than people realize, you just can't see it easily unless the barrel is shiny.
Exactly, it's the nature of the beast. These are military style rifles, with military style tolerances. If it's not leaking gas around the FSB, it's leaking around the gas tube. Simply put, they just normally leak a little, like I said in my first post.

I'd suggest most posters with Parkerized "non-leaking" guns would be quite surprised if they pulled the handguards and wiped the barrel around the FSB/gas block with a white rag and a little solvent . . . LOL, lots of manufacturers would have their phones ringing off the hook today . . .I only have one "shiny barrel" upper and it shows a little of this, not as bad as the OP but a small amount.

As EShell says, that looks like oil from assembly. The gas leaking out may be a very small amount but it's blowing this oil out. I would expect that to go away after a short time.
Agreed. The SS barrel makes it easy to see and the excess dirty oil makes it look like the huge disaster that it's really not.

MyRoad
September 10, 2008, 10:07 AM
This morning I sent an email and the pic to DPMS, I'll let y'all know what their response is.

taliv
September 10, 2008, 10:10 AM
cool. have fun at the wounded warrior shoot

MyRoad
September 10, 2008, 10:42 AM
DPMS CS responded in under 30 minutes, which in itself is notable:

That is common to see that blow by at the gas block area. This is
because the front sight is not a press on item. It is a little hard to
clean off that carbon, but you have nothing to worry about.
If you have any questions please feel free to contact [me].

Tarvis
September 10, 2008, 11:58 AM
if the hole cloggs up, eventually , it will work its way into the gas tube causing feeding and extraction problems
Um, you realize the same stuff that came out from under the FSB is blowing through the gas tube already, right? Even if it did start to "work its way" into the gas tube, the 20,000 psi or whatever it gets up to is not going to be hindered by a little crud under the FSB.

KingTiger
September 10, 2008, 12:16 PM
I've got a RRA with SS bull barrel and noticed a similar leak/discharge also. I mainly shoot it suppressed (AAC M4-2000) and just figured it was a blow back issue from the suppressor. Good info, thanks.

Funderb
September 10, 2008, 12:19 PM
looks like we got a weeper,

jus throw some duct tape on there and youll be right as rain.

Omnivore
September 10, 2008, 09:03 PM
The same thing happens on both my ARs (factory Colt and RRA) and both my M1As. No problem. Look around closely and you'll see gas coming out all over the place. It's part of the animal. The stainless barrel just makes it more visible, or you may not have noticed so soon.

longdayjake
September 10, 2008, 09:49 PM
I found out that my gun did it when I bought some of that camo medical wrap to hunt coyotes with. After I took it off there was black stuff where the fsb is. My gun shoots super well so I didn't worry about it.

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