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Old July 15, 2013, 09:21 AM   #15
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
Mobuck, and others, here's why most factory installed barrels change point of impact when they heat up.

The receiver face is not squared up with the barrel tenon threads. When the barrel torqued in, it bears hard at one point. When it and the receiver heat up, the expanding metal puts a greater stress point where that place is and that makes the barrel bend.

Some folks have squared up their factory receiver faces by turning off 5 thousandths, then putting in a .005" shim between it and the barrel so it clocks in to keep headspace correct. Such changes get rid of shots walking as the barrel heats up.

"Sporter weight" barrels are the norm in M1 and M14 rifles, yet when match conditioned, such rifles and those barrels hold zero even when fired 24 times in 50 seconds. They've been tested in machine rests and have shot sub MOA at 600 yards so stressed. And they'll shoot 1/2 MOA at 300 yards fired 10 times in 60 seconds. One 7.62 NATO chambered Garand put all 8 shots from a full clip in 40 seconds into 7/8ths inch at 300 yards when tested starting with a cold barrel.

And most sporter weight 22 and 24 inch barrels are stiffer than Palma rifle's thicker 30 inch long barrels. Those long ones are oft times shot once every 15 seconds for 20 shots and they'll shoot 1/2 to 5/8 MOA at 800 yards for the whole shot string.
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