can just looking down the barrel tell everything?

I would visually inspect the muzzle and the rifling at the muzzle. If the rifling is very faint or gone, I doubt it will shoot very well.

From what i've heard you can't.  You need a borescope ($600-700) to be able to really tell.  The area of rifling directly in front of the chamber is where a barrel starts to wear out.  Of course even if you see some pitting or whatever that doesn't mean that the barrel won't shoot, just that the odds are against it.  Of course a worn muzzle will hurt accuracy but the damage can usually be easily repaired.

It's easier to inspect the target.  If the barrel gives nice, tight groups it's not shot out.  If the bullets put keyhole shape holes in the paper it is shotout.

If the groups are merely big, clean the barrel and test again.

Sure you can borescope the barrel, if you can find one that small, otherwise just do the gage checks at the end of Chapter 3 in the -23&P.

-- Chuck

[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=16164[/img]

Pic stole from "Tweak"

I'm guessing extended firing. Look how parts of the handguards are melted.

This barrel will fail a gage check.....

-- Chuck

JMO,
    I bought a barrel from SARCO, that was advertised as "Shot Out" for around $40 for a .22 upper project and when I got it I couldn't find a thing wrong with it! Nice clean chamber, nice sharp rifling, nice finish on the Pencil type light weight barrel. It even came with the A2 flash hider, the A2 front sight and handguard cap and barrel nut! I looked that barrel over and over again and could find nothing wrong with it -- then I noticed a funny shadow ring just an inch or two back from the muzzle. Sure enough it had a ringed bore. If this barrel was at a gun show with no note on it saying it was "Shot-Out" I might have paid good money for it. I guess what I'm trying to say is sometimes the condition of the barrel is easy to see and sometimes it's not. The only good test, short of sending it to a gunsmith, is try shooting it.

Escaping gas would have also melted the HG's.