gonna have access to a bore scope

O

oley55

New member
Good news, in a couple weeks I will have the opportunity to inspect my bore with a bore scope. The barrel in question is possibly an ER Shaw (but no markings), 1:8, 24" stainless, heavy barrel, in 5.56. As per earlier posts, this barrel starts fouling after only 12-15 rounds, and is throwing flyers. http://thefiringline.com/forums/showthread.php?t=563239

Although I expect the owner/operator of the bore scope will be able to interpret the images, I would like to be as educated as possible in advance. If the barrel checks out OK, we are going to cut a new crown (and I may cut it down to 20").

What should I be looking for, and how will I know if what I see is good, marginal, or bad.

Is there a source out there that will show images of a barrel with varying degrees of throat erosion, and etc..
 
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A bore scope is just a light.
24" SS doesn't describe it enough. What the contour?
Images of a barrel won't tell you anything. You need proper gauges. And a barrel doesn't throw anything. Flyers have multiple causes.
I'd be inclined to contact Shaw(their barrels aren't terribly expensive) and ask if they've ever sold an unmarked barrel.
http://ershawbarrels.com/contact-information.php
 
And a barrel doesn't throw anything.
Click to expand...

was that offered as thoughtful information or.............what?

Not at all clear how the barrel contour will help interpret the images seen through a bore scope.

I provided the basic barrel description as I expect the throat area for straight wall chambered rifles, rim fire, bolt, autos and etc will be different. Would I look for something in particular in an AR versus a bolt action?

I have done some google searches and found a couple items showing heat cracking, pitting, and fouling, but have not been able to find a pic or image depicting throat erosion.
 
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found a couple items showing heat cracking, pitting, and fouling, but have not been able to find a pic or image depicting throat erosion.
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Throat erosion, easy to keep when using a tapered gage, problem the tapered gage is round, it has a tapper. Anything that is round and has a tapper is called a cone.

Heat cracking, the chamber contains rapidly expanding hot high pressure metal cutting gas, that is the reason I want my case to cover all of the chamber.

I do not covet head space gages, I use the ones I have as transfers and standards, my favorite head space gages are the ones that are too long, those are the ones that will not allow the bolt to close, not a correction but worded differently, 'should not allow the bolt to close'. And that is the reason they are my favorite.

F. Guffey
 
If you have really scrubbed out the copper fouling

And you are still getting flyers from that barrel, it might be done for. I took a gun to a smith for bore scoping, and he said it looked fine. BUT. That gun was producing keyholes and flyers. Using loads that had previously worked just fine. After much frustration and many trips to the range, I finally gave up on that gun. So you may not see anything really obvious with that scope.
 
Bore scope found my problem

I had a Beretta pistol that would not group. Looked at it with a bore scope and saw what looked like a metal blemish inside the barrel. Took a polished steel rod and slid down the barrel over what I thought was a metal blemish. When the rod went over the blemish it made a clicking sound. I estimate a .001" to a .002" ridge in the barrel. Sent it back to Beretta and they put a new barrel in it. Groups nicely now.:)
 
What you can see in a borescope is the fouling itself, if there's any left, and you can get a good look at the surface texture to see pitting. You can also see the throat cracks Mr. Guffey mentioned.

Those cracks are, as he said, caused by hot gas. The thermal effusivity of the metal is low enough that heat doesn't travel very far into its surface in the time it takes a bullet to get out. The surface is usually only penetrated a couple thousandths of an inch by heat before pressure and temperature drop due to the bullet exiting. After that, the remaining heat diffuses out into the barrel. This means the surface of the bore expands faster than the metal under it, then cools and contracts sooner than the metal underneath it. This back and forth differential expansion and contraction eventually fatigues the surface so it cracks, leaving a surface that resembles alligator skin. A that point the little squares of alligator surface become vulnerable to being blown off by gas and powder particles, causing the appearance of erosion. Often, they don't come off evenly, so the throat becomes asymmetrical. This forces bullets to engrave at a slight tilt, which reduces precision of shot placement.

If you have a badly alligatored throat, you will see that and you will see that the pattern stops a short distance down the bore. That is because the bullet only travels an inch or so by the time the pressure and temperature peak, so the rest of the bore doesn't see the same extremes, and, because the bullet is then moving faster, the extremes it does see are for shorter times. Based on throat appearance you can decide if the barrel needs to be set back and rechambered to give it a fresh start. You can see the surface condition of the rest of the bore and see if it needs further firelapping or other smoothing.

If you decide to cut the barrel back, you want to do any rechambering first. Afterward, before going all the way to 20", you might want to try the 21¾" "magic" barrel length found in the Houston Warehouse experiments, just to see if it works well for you, too?
 
Thanks Guys for the replies. I have been on the road and this is my first access to the net. I sure am looking forward to seeing what the scope reveals.
 
Nick,

thanks for the link to the Houston Warehouse Experiments article. A very interesting read and a good bit over my head and out of my league. Regardless, I have saved the link and will need to reread it a few more times.

On the subject of accurately measuring barrel length, on the breach end what is the measuring point? I presume the measuring point for an AR15 barrel does not include the barrel extension.

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just did a search and found the barrel should be measured by sliding a dowel or rod down the barrel until it stops against a closed bolt's face. Then mark and measure.
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Is that right?
 
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That is the LEGAL definition of barrel length.

Some ballistics calculations use swept length or actual bullet travel.

You can run a bore scope through a good shooting barrel and scare yourself into thinking it worthless.
 
Another thing you can do is slug the bore. This will not only give you a good idea of ideal bullet diameter for that barrel, you will be able to feel any areas of possible concern whilst pushing the slug through. A tight or loose area can be bad.
 
Oley,

Yes. From the standpoint of the Houston Warehouse experiments, like SAAMI, you will measure the distance from the breech end (boltface with bolt closed) to a distance flush with the end of the crown. The idea hear is that this is the length that produces the right barrel time.
 
oley,

I am including an article that appeared in Precision Shooting Magazine on rifle bore cleaning. I'm not trying to sell what the article suggested, but if you look at the end of the pdf file, you will see some images taken while using a Hawkeye Bore Scope. Helps you prepare for what you might see.
 

Attachments

a bit disappointed

access to a bore scope didn't work out. Regardless, I am confident this barrel is as clean as I am ever going to get it.
 
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