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wtf is this thing in my barrel? (Page 1 of 2)
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Posted: 2/9/2026 3:06:37 PM EDT
[Last Edit: AR-Zen][Edited]
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I've noticed some decline in my rifle accuracy. Not much, maybe 0.25 to 0.5 MOA. So, I decided to invest in a barrel scope, just to see what's inside. I've never used the barrel scope before. I've cleaned the rifle thoroughly before inspecting the barrel with the scope. So, I did not expect to see anything unusual, other than maybe some traces of carbon and copper. To my horror, I saw this lump of whatever that is, which looks like cancer within the bore. Here is the video of the spot: https://i.imgur.com/e1DGHsI.mp4 WTF is this thing? |
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Originally Posted By chaas67: As those wiser than me have said, you will fuck up a barrel quicker by having a borescope than not. 😁 the only thing i use mine for is to confirm gas block alignment in a new build. And find screws that i drop in tiny crevices 🤣 Yes, please God, stop selling these things. They cause more hate and discontent than even an anti-ICE demonstration. |
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Originally Posted By AR-Zen: I shoot consistently 0.5-1.0 MOA groups. When they become 0.75-1.25 MOA groups, I take notice. And you're getting those sub-MOA groups from a Sig M400 Tread. |
Point shooting will give you monkeypox. - John_Wayne777
The Emu War could have been won if the Australians used red dots on their handguns.
The Emu War could have been won if the Australians used red dots on their handguns.
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Originally Posted By 45-Seventy: You have an impressive skill level for someone who doesn't understand how an AR type rifle functions. And you're getting those sub-MOA groups from a Sig M400 Tread. Attached File |
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Originally Posted By Frens: Got it. Btw here is how the gas port looks like in a barrel… gas port wear will increase over time of course https://cdn-fastly.thefirearmblog.com/media/2024/05/15/14168233/ever-wondered-what-80-100k-rounds-fired-does-to-an-ar-15-barrel.jpg?size=720x845&nocrop=1 Originally Posted By Frens: Originally Posted By AR-Zen: I shoot consistently 0.5-1.0 MOA groups. When they become 0.75-1.25 MOA groups, I take notice. Got it. Btw here is how the gas port looks like in a barrel… gas port wear will increase over time of course https://cdn-fastly.thefirearmblog.com/media/2024/05/15/14168233/ever-wondered-what-80-100k-rounds-fired-does-to-an-ar-15-barrel.jpg?size=720x845&nocrop=1 Is there some kind of fluid dynamics reason that the port erosion only happens on one side? |
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Originally Posted By AR-Zen: That’s correct. You have an extraordinary level of skill combined with what is perhaps the most accurate example of a rack-grade AR type rifle to have ever been produced. |
Point shooting will give you monkeypox. - John_Wayne777
The Emu War could have been won if the Australians used red dots on their handguns.
The Emu War could have been won if the Australians used red dots on their handguns.
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Originally Posted By gtsteve03: Is there some kind of fluid dynamics reason that the port erosion only happens on one side? |
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The two high wear spots on the barrels are the throat and the gas port. The throat is where the bullet just starts catching on the track of the rifling. That particular area will eventually turn into alligator bed. The gas port will erode towards the muzzle so you'll eventually see a huge dent into the gas port as the barrel wears. Those black streaks you see is carbon build up. You can probably knock most of it off simply by using a quality bore cleaner like Hoppes or similar. As I said in the other thread you made, I think sorry if not, but barrels are wear items. You should have a spare barrel and bolt/complete bcg on hand. Of course this doesn't mean the barrel needs to be swapped as it has many more 1000s of rounds. |
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Originally Posted By 45-Seventy: You have an impressive skill level for someone who doesn't understand how an AR type rifle functions. And you're getting those sub-MOA groups from a Sig M400 Tread. Originally Posted By 45-Seventy: Originally Posted By AR-Zen: I shoot consistently 0.5-1.0 MOA groups. When they become 0.75-1.25 MOA groups, I take notice. You have an impressive skill level for someone who doesn't understand how an AR type rifle functions. And you're getting those sub-MOA groups from a Sig M400 Tread. 
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"An age of glory passed like a lightning flash. The mandate of heaven passed from you but you didn't see. Times change and power passes. It is the pity of the world."
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Originally Posted By AR-Zen: After another round of cleaning, it looks a little less scary, although it still evokes the visions of a black hole, and a malignant tumor. Does this wear and tear around the gas port cause accuracy issues, or is it normal? https://i.imgur.com/AJC5GRH.png Yes that is normal and will continue to worsen as you shoot. As I said in my other response that's not where the accuracy is counted. It's the throat which is the front part of the barrel where the rifiling starts. That area is where a barrel's accuracy dies. The only way to prevent it is to simply not shoot at all. Firing at a much slower rate and not causing the barrel to heat will be the main factor behind prolong barrel life. But I wouldn't stress it as you'll probably never shoot enough for it to get affected. Do yourself a favor and toss the borescope. Go try shooting it again with the same ammo. It might have just been a bad day or such. As someone who shot out two barrels, I can safely say the decline is not noticeable but suddenly. There is nothing you can do other than clean it, and/or replace it and/or never shoot it. |
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Originally Posted By j3_: Is there many or more than one of those things in the same barrel? Nothing as dramatic as what I already posted. There is some horror inside the muzzle device. Also, as dalle predicted, the scope reveals quite clearly that most of the carbon and copper deposits are near the throat of the barrel. That gives me the idea about where I need to focus on while cleaning. |
 10,000 Rounds - BCM Accuracy Test Here's a good video on what you'll see as your barrel wears. He has 10,000 rounds through it and never cleaned it. Check out the 3:54 mark on how the gas port erosion will eventually look like as the barrel wears in. Then look at about the 6:10 mark for how the throat area will look like. Some will degrade more. He also shows what a new barrel would look like and that starts at 8:33 mark for the gas port and at the 9:28 mark on the throat of a new barrel. It's been factory test fired so that is why there are some build up. In other words your barrel is perfectly fine. I do not know about how you're figuring out the MOA thing with it but I think you're just looking into it too much. |
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Originally Posted By dalle0001: In other words your barrel is perfectly fine. Yep, I've spent like 4 hours deep-cleaning the barrel and got most of the carbon and copper out. Here is how the accuracy looks like now. If we exclude the 1.3" group, it would be 0.6-0.95 MOA, which I can accept as good accuracy. 
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Originally Posted By AR-Zen: I shoot consistently 0.5-1.0 MOA groups. When they become 0.75-1.25 MOA groups, I take notice. Originally Posted By AR-Zen: Originally Posted By Frens: Btw I’m amazed by the ability to notice .25 MOA variations in your groups I shoot consistently 0.5-1.0 MOA groups. When they become 0.75-1.25 MOA groups, I take notice. Yet you have no idea you had a gas port in your barrel? Attached File |
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Originally Posted By Justintime2: Yet you have no idea you had a gas port in your barrel? You don't need to know how pianos are built to be a world-class concert piano player. I knew I had a gas port, I just didn't expect it to look like a monster with a bore scope. |
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Originally Posted By AR-Zen: You don't need to know how pianos are built to be a world-class concert piano player. I knew I had a gas port, I just didn't expect it to look like a monster with a bore scope. Originally Posted By AR-Zen: Originally Posted By Justintime2: Yet you have no idea you had a gas port in your barrel? You don't need to know how pianos are built to be a world-class concert piano player. I knew I had a gas port, I just didn't expect it to look like a monster with a bore scope. A world class piano player will know the parts in their instrument and will know when it doesn't sound right. |
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No ill will or insults here, but it is a very good idea to take the time to learn the parts of your AR, how it works, and WHY it works. It will help you diagnose problems faster and keep you and those around you safer. It is a machine and so it can break, even in potentially catastrophic manner, but so also it can be diagnosed and repaired in a logical way. Even if you don't gain the skills to do all the work yourself, it is good knowledge to have, if for no other reason than improved safety. For basics, just watch a handful of youtube videos with animated diagrams, even. |
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Originally Posted By AR-Zen: Yep, I've spent like 4 hours deep-cleaning the barrel and got most of the carbon and copper out. Here is how the accuracy looks like now. If we exclude the 1.3" group, it would be 0.6-0.95 MOA, which I can accept as good accuracy. https://i.imgur.com/VeH1O5Y.jpeg Why would you exclude a group simply because it shows your group size variation is around 100%? |
Point shooting will give you monkeypox. - John_Wayne777
The Emu War could have been won if the Australians used red dots on their handguns.
The Emu War could have been won if the Australians used red dots on their handguns.
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Originally Posted By 45-Seventy: Why would you exclude a group simply because it shows your group size variation is around 100%? My standard of accuracy is 5 groups of 5 shots each (25 shots total), with group sizes of 0.5 to 1.0 MOA. What I said was that without the 1.3" group, I would have met that standard of accuracy. The existence of the 1.3" group clearly indicates that I have not returned to that level of accuracy after deep cleaning, although it certainly looks better than before the deep cleaning. |
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Originally Posted By AR-Zen: My standard of accuracy is 5 groups of 5 shots each (25 shots total), with group sizes of 0.5 to 1.0 MOA. What I said was that without the 1.3" group, I would have met that standard of accuracy. The existence of the 1.3" group clearly indicates that I have not returned to that level of accuracy after deep cleaning, although it certainly looks better than before the deep cleaning. I was looking to see or know what ammo was giving .5 moa groupings. The links are showing moa groupings. Or am I mistaken. |
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Originally Posted By AR-Zen: That’s correct. Originally Posted By AR-Zen: Originally Posted By 45-Seventy: And you're getting those sub-MOA groups from a Sig M400 Tread. That’s correct. Good news fellow firearms enthusiast, there’s a thread just for you! https://www.ar15.com/forums/precision-rifles/-ARFCOM-1-MOA-ALL-DAY-LONG-Challenge-/17-51/ Put up or shut up. |
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Wow OP. This is…special. Not quite as special as the guy on TOS years ago who “converted” his carbine gas Rifle into a midlength using a clamp on gas block without drilling a midlength gas port, without welding or covering the carbine gas port, and using a midlength gas tube. His single shot blew the top handguard off and he was incredulous that it would do such a thing. |
wtf is this thing in my barrel? (Page 1 of 2)
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