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Old August 30, 2012, 03:04 PM   #15
Bart B.
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Join Date: February 15, 2009
Posts: 8,927
Kraig's made some good comments about barrels overheating and not changing point of impact. Here's supporting comments.

Lake City Army Ammo Plant tests rifle ammo shooting 200 to 300 shot groups at 600 yards. With a good batch of 7.62 NATO match ammo, they'll all go inside 6.5 inches. All shots are fired when the wind's calm and about 10 to 15 seconds apart.

Those Infantry Trophy (Rattle-Battle) matches Kraig mentioned; each rifleman on a team typically did the following with his Garand (and later with M14's and M16's)

At each range of 600 and 500 yards prone then 300 yards sitting, getting into position and aiming at where the targets will come up then taking two deep breaths when the range officer commands "Load and be ready" and loads a full clip. When he sees his target start up over the safety berm he shoots 8 rounds at it, reloads, shoots 8 more then reloads and shoots the last full clip of 8 watching the silhouette target start down a second after his last round's fired. All 24 rounds in 50 seconds. That's under 2 seconds between shots with reloading and going back into position and taking two deep breaths taking about 3 to 4 seconds twice. Any left over ammo's divvied up among the 6-man team where they move to 200 yards and shoot standing. You get 4 points per hit on the silhouette at 600, 3 at 500, 2 at 300 and 1 at 200. If all targets having more than six hits, you get extra points. There's 8 targets; usually two shooters splits their rounds between two targets; they're called a "swing man"

There's been more than a few 2nd degree burns on bare necks from super hot barrels touching them while being mishandled after firing a string. And good Rattle-Battle rifleman can put all their shots inside 12 inches at 600 yards, 10 at 500 and 8 at 300 and 200. They use their regular match grade barrels. And that doesn't cause any more wear than regular rapid matches shooting 10 shots in 60 or 70 seconds.

If you barrel shoots bullet to some other point of impact as it heats up, there's three main causes and one that's not part of the hardware. . . .

The barrel's not stress relieved properly; often is the case with cheap aftermarket barrels.

The receiver face wasn't squared up when the barrel was fitted; the high point puts a stress line down the barrel at that point when the barrel heats up expanding and bending on that stress line axis.

The barrel expanding over an epoxy bedding pad under the chamber puts vertical stress on it; the vertical barrel whip when fired gets different and bullets don't leave the same tiny range of angles they would normally do.

And sometimes the shooter doesn't keep the same exact position shot after shot after shot. . . . .

Last edited by Bart B.; August 30, 2012 at 03:22 PM.
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