I've heard that once a barrel heats up to a certain temperature and then cools back down it physically deforms a little bit (the metal doesn't go back the same way it was before). Is this true, and if so what temperature must be reached and how much would this diminish accuracy? Would the effects be more noticeable in a lightweight (AR) barrel? I understand that as barrels heat up they can lose accuracy, but is this permanent?
Barrel Heat and Accuracy (and Lightweight Barrels)
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buck460XVR
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While I've had barrels get hot and lose accuracy(esp. lightweight stainless), they have always gone back to zero when cooled.
I guess it would depend on how hot. From a hunting rifle perspective some of the very lightweight barrels shoot very well for 1-3 shots then a sub-1" group starts to open up dramatically. Often as much as 3-4" for shots 4 and 5. But after cooling the accuracy has always returned for me.
On military rifles that are often shot hundreds if not thousands of rounds before being allowed to cool then the damage could be permanent.
On military rifles that are often shot hundreds if not thousands of rounds before being allowed to cool then the damage could be permanent.
Sav .250
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There are times when ," What I`ve heard" is a crock .
Buck460XVR ......... Correct answer.
Buck460XVR ......... Correct answer.
Art Eatman
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After some sixty-five years of centerfire, I've now learned a new "I heard..." 
http://www.fieldandstream.com/blogs/gun-nuts/2012/08/how-rifle-barrels-die
http://www.military.com/video/guns/machine-guns/how-to-melt-the-barrel-of-your-mg/658467292001/
http://gunsmagazine.com/rifle-barrel-burn-out/
Get it hot enough and you'll damage the barrel. There are examples of military machine guns getting hot enough to actually bend. But in most civilian uses this won't be a factor.
The most common cause is the heat eroding the rifling and causing poor accuracy.
http://www.military.com/video/guns/machine-guns/how-to-melt-the-barrel-of-your-mg/658467292001/
http://gunsmagazine.com/rifle-barrel-burn-out/
Get it hot enough and you'll damage the barrel. There are examples of military machine guns getting hot enough to actually bend. But in most civilian uses this won't be a factor.
The most common cause is the heat eroding the rifling and causing poor accuracy.
Competitive shooters putting 10 rounds dowrange in 60 seconds with light, skinny barrels see no accuracy change doing that then again a few minutes later.
7.62 NATO chambered Garands tested for accuracy in an accuracy cradle put three full clips (24 rounds) into 2 inches on the 300 yard target with good commercial match ammo. All shots fired about 8 seconds apart.
Barrels properly heat treated and fit to squared up faces on receivers don't bend from the heat caused by most sporting rifle use; even rapid firing many shots 15 to 20 seconds apart. If bullet impact shifts from barrel heat, that's because the barrel's hard against one point around its shoulder on the receiver. Both barrel and receiver expand from heat, but that high point puts a stress line on it that bends the barrel.
Have your receiver faced off a few thousandths, then a few thousandths shim put in between barrel and receiver so the barrel clocks in for proper heaadspace.
7.62 NATO chambered Garands tested for accuracy in an accuracy cradle put three full clips (24 rounds) into 2 inches on the 300 yard target with good commercial match ammo. All shots fired about 8 seconds apart.
Barrels properly heat treated and fit to squared up faces on receivers don't bend from the heat caused by most sporting rifle use; even rapid firing many shots 15 to 20 seconds apart. If bullet impact shifts from barrel heat, that's because the barrel's hard against one point around its shoulder on the receiver. Both barrel and receiver expand from heat, but that high point puts a stress line on it that bends the barrel.
Have your receiver faced off a few thousandths, then a few thousandths shim put in between barrel and receiver so the barrel clocks in for proper heaadspace.
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