AR15 Barrel Inspection w/ Video Articulating Borescope

AR/M4 AR Technical Discussion
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Had a chance to demo a borescope recently, and thought of running it through my AR. Unfortunately, a new or another abused AR wasn’t readily available to compare and contrast with. Additionally the borescope didn’t include a 90 degree probe for inspections perpendicular to the bore axis. Nonetheless, it was definitely interesting and cool to see the rifle from a detailed and different perspective that majority of shooters may never have a opportunity to see.

The AR inspected is an early Smith & Wesson MP15T, assembled before 2007, serial number in the fifty five hundreds, originally with an aluminum gas block non-pinned, and with a non-drop free Pmags receiver featuring little or no bevel of the magazine well. It’s essentially a Stag before S&W brought their AR production in-house. Since 07’, the magazine well has been bevel, the low profile gas block was replaced, pinned, and barrel was refinished with Alumahyde, but still is a 1:9 government profile 16" 4140 chrome-lined carbine-length barrel with rifle feed ramps, w/ over 16k rounds over the coarse of 5 years. However, majority of that count is with 22s, ~10,000 with a drop in conversion kit, and 5k rounds of .223 - consisting mostly of steel case ammunition, plus 1k of 5.56 either of XM193 or M855, and the most severe abuse the barrel took was a near continuous fire, with perhaps 400 rounds during a carbine coarse running back to back drills, without sufficient time for the barrel to return to ambient temperature.

Chamber Area

Throat



Gas Port

Videos:


Haven’t had the time to really dissect the videos or pictures, but I did notice it captured the bit a carbon build up that I wasn’t able to get it behind the chamber star area directly in front of the ejection port, and residual copper residue even after allowing a solvent to sit over night. It also seems to me the gas port is unusually large, but don’t have any other AR to compare it with, and without a 90 degree tip can’t make a comment with respect to worn rifling. But chamber area looks fine, expect perhaps at the throat seems like there some pitting right at the periphery of where the bullet would separate at the neck of the case.

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Awesome! Ive always wondered how the barrel would look through a bore scope. How many roundsnhave you had through it? Looks like you have a bit of port errosion going. This being the first time Ive ever seen the image from a borescope, Im Not sure how severe that is. Im thinking it’s still minimal, if not average.

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I also have no idea how its supposed to look, but the gas port looks a little eroded toward the muzzle end, and I dont know if it is burrs or something else, but the little white flecks between the gas port and the muzzle caught my eye.

It would be cool to compare lots of different barrels.

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I’d love to do that to all of my barrels. That’s pretty cool to see inside there.

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I love it. Thanks for the inside view.

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Interesting how well you can see the reamer and rifling tool marks. How well did you scrub this barrel before scoping it?

Until that day,
Darkop

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Damn, that is a lot of tool chatter on the lands. Everything looks ugly under magnification though.

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This is the first borescope pics I’ve seen to but I’m not so sure that’s port erosion you’re seeing. Looks to me like copper residue build-up on the muzzle side, as if every bullet that passed it had a little of the copper jacket scraped off on that edge & left behind. Then I read your post about having some 10k 22lr through that barrel & my theory seems to make even more sense. Can you say, “copper wash?”

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Same here, as soon as I demoed it, I got excited and immediately thought, man I need to grab my AR and run this through it!

See original post. ~16,000 rd = 6,000 [.223/5.56] + 10,000 rd [22]

I tried googling bore scope and AR, to see if any one else had posted something similiar, but what I got were bore scope pictures with a perpendicular probe to look at the rifling. Without another well used AR to compare to, I am not sure if it is port erosion either. Where would the wear pattern form? Would the erosion be uniform across the port, closer to the chamber or as shown above near the muzzle end? Luckily, I am not aware of any performance issues thus far, as I haven’t seen a noticeable degradation of accuracy or precision, with a increasing group size or shifting of zero, or otherwise.

I do have other videos but haven’t uploaded them yet, of the bolt carrier and gas key, as well as some pistol barrels I ran the scope through, I’ll see if I can post them later tonight. There’s a pretty cool one showing the bolt face and how it locks in the chamber.

Not at all actually, sort of last minute deal, grabbed the AR and left. But the barrel is cleaned after each range session. Quick cleaning consist of a blast with brake parts cleaner, while scrubbing with a chamber brush, immediately followed by WD40 just to quickly remove the gunk, followed by another shot of brake cleaner, then a bore snake with Hoppes. If time permits, I let it sit, while I take care of other parts, components, and guns, and I come back to the AR barrel last with a nylon coated cleaning rod, 22 jag with dry and wet patches till they come out decently white, after a couple thousand, I’d follow up with some copper solvent.

No kidding. To the naked eye looking down the chamber and barrel, it looks like a mirror finish, with the light reflecting down the barrel. I didn’t expect to find noticeable tool marks, not sure if it’s because the chrome lining exaggerates it, but interestingly the other barrels I ran the scope through, the pistol ones I had available, the tool marks are hardly noticeable at all.

That certainly could be possible, subsequent rounds promoted the build up of copper. However, after going back through the other videos, there seems to be a symmetric pattern to what looks like an indentation to the edge of the gas port towards the muzzle end.

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Here are some additional videos shot by the borescope:

Young’s NM Bolt Carrier and Gas Key

Rear Chamber Lugs View

Bolt Locking and Unlocking In Chamber

Chamber Neck and Throat Area

At first I thought this was pitting area where the cartridge case meets with the bullet, the small area that would touch the small front profile of the case neck, but it looks too uniform. Could this be the result of shooting rounds with a cannelure?

Another View of the Gas Port

Glock 23 Gen 4 Barrel

Lonewolf Glock 23 Conversion Barrel 40 to 9 Threaded

Lonewolf Glock 23 Threaded 40 Barrel

Keltec 380 AT Barrel

XD45 Compact Barrel

XDm 9 4.5" Barrel

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button rifled?

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The chatter marks are the first thing I noticed as well, mostly because I have no idea what any of the other potential wear things look like - erosion…

Try some CopperZilla. Run a wet patch down the barrel and let it sit for 10 minutes. Then have fun pulling nasty green patches out for the next 10.

Be interesting to see the difference between a CHF barrel and a Chrome lined stainless.

ON EDIT - After thought. I don’t wonder if it would affect the accuracy removing any buildup in the chatter marks down the bore. They are just going to get loaded up again. Moly coated rounds maybe?

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Looks like my last Colonoscopy…LOL

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Nice shots.

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I would be really interested in seeing the comparison of this to a Hammer forged barrel. How the tool marks look, etc.

Either way, very cool.

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If your colon had a twist rate… Problems.

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Great stuff-- nothing like shrinking ones self to 1/8" height and then exploring the cave that is your gun barrel! Thanks for posting that.

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Those pics of the bolt face…Is that crud on the bolt face or is it pitted? I can’t really tell…

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Gas port erosion is normal, they all have it.
Chatter is caused partially by pulling the button through and partially from honing of the bore. Most all AR barrels have the chatter marks unless the bore is lapped like most match grade barrels.
Believe it or not the chatter itself does not effect accuracy, I have seen barrels just like these that will shoot under 1/2" groups and some lapped match barrels that will not shoot under 3/4".
There are other things that effect accuracy more than the finish in the barrel. A straight hole is one thing, a good crown, a chamber that is concentric and proper stress relief is more important than the finish.
Just because the barrel is lapped doesn’t mean it will shoot better. I have seen a ton of “match” barrels that don’t have straight bores, when indicated at each end and spun in a lathe the bore looks like a banana whipping around. A lapped barrel may not copper foul as much because the sharp edges in an unlapped barrel may strip copper from the bullets.
If you want an accurate barrel you must keep the copper cleaned out of the bore.
In over 15 years of looking through barrels I can say 1 thing, I have never seen a bad Krieger. Not saying some aren’t drilled crooked it’s just that they dont let them out of the plant that way. If they are crooked then they cut them off and offer them as a shorter blank.

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Interesting. The only hammer forged barreled AR I have, is also by far the easiest to get the copper out of, if it collects any at all. This explains why.