Wandering Shots as Barrel Heats Up - Page 2

big al hunter · December 1, 2012, 10:29 AM

Bart, the table testing you described will also show a bent barrel. Did he do anything else to check for straight? Was the win 70 barrel on an action? If so how did it shoot? If it shoots well that would show us if slight differences affect accuracy much.

I would expect that larger differences in lighter barrels would make more of a change in accuracy, particularly as the barrel heats up.

1stmar · December 2, 2012, 07:28 PM

Interesting Bart, I wonder if gs perform any similar tests before installing... It would be preferable to have the heavy side at the top (imo) when mounted. This would likely cause vertical stringing as oppose to horizontal.

Bart B. · December 3, 2012, 02:36 PM

Big Al, the Obermeyer barrel not shanked, chambered nor crowned when tabled for the roll test. It was later chambered for the .30-.338 round and easily shot about 1/2 MOA at 1000 for 20 shot test groups with each shot fired about 25 seconds apart. So it got pretty hot from cold to whatever its temperature was.

The Winchester factory barrel was not in an action. It looked and tested pretty straight with only a few thousandths runout in its middle with each end in a V block. Looked straight, too, but the three tapers on it made it hard to check.

Regarding lighter barrels that are bent. All the M1 and M14 match conditioned rifles used for service rifle matches have the barrel bent down a bit by the stock ferrule's fit to the barrel's lower band. Their receivers are bedded such that the barrel in it rests about 3/16th to 1/4th inch more up from the stock ferrule than where it is when the hardware's put on the barrel and it's assembled into the stock ferrule when put together. This pulls the barrel down at that point at about 20 to 40 pounds of force depending on the rifle type. Barrels so set up do bend down relative to their chamber axis. But its only a few thousandths of an inch at that point becaus the stock fore end gets bent up at the same time. They all drove tacks when tested for accuracy, so their bent barrels heating up in a 20 to 30 shot string didn't suffer any point of impact change.

Gosh, that happened decades ago. 'Tis hard remembering the details of such tests back then.

Erno86 · December 4, 2012, 05:35 PM

A gun barrel...that is placed in the hot sun ---will heat up the barrel on one side --- which will cause a different point of impact, to a gun that was not placed in the sun.

December 1, 2012, 10:29 AM	#26
big al hunter Senior Member Join Date: March 12, 2011 Location: Washington state Posts: 1,558	Bart, the table testing you described will also show a bent barrel. Did he do anything else to check for straight? Was the win 70 barrel on an action? If so how did it shoot? If it shoots well that would show us if slight differences affect accuracy much. I would expect that larger differences in lighter barrels would make more of a change in accuracy, particularly as the barrel heats up. __________________ You can't fix stupid....however ignorance can be cured through education!

December 3, 2012, 02:36 PM	#28
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Big Al, the Obermeyer barrel not shanked, chambered nor crowned when tabled for the roll test. It was later chambered for the .30-.338 round and easily shot about 1/2 MOA at 1000 for 20 shot test groups with each shot fired about 25 seconds apart. So it got pretty hot from cold to whatever its temperature was. The Winchester factory barrel was not in an action. It looked and tested pretty straight with only a few thousandths runout in its middle with each end in a V block. Looked straight, too, but the three tapers on it made it hard to check. Regarding lighter barrels that are bent. All the M1 and M14 match conditioned rifles used for service rifle matches have the barrel bent down a bit by the stock ferrule's fit to the barrel's lower band. Their receivers are bedded such that the barrel in it rests about 3/16th to 1/4th inch more up from the stock ferrule than where it is when the hardware's put on the barrel and it's assembled into the stock ferrule when put together. This pulls the barrel down at that point at about 20 to 40 pounds of force depending on the rifle type. Barrels so set up do bend down relative to their chamber axis. But its only a few thousandths of an inch at that point becaus the stock fore end gets bent up at the same time. They all drove tacks when tested for accuracy, so their bent barrels heating up in a 20 to 30 shot string didn't suffer any point of impact change. Gosh, that happened decades ago. 'Tis hard remembering the details of such tests back then. Last edited by Bart B.; December 3, 2012 at 02:44 PM.

December 2, 2012, 07:28 PM	#27
1stmar Senior Member Join Date: March 21, 2012 Location: Connecticut Posts: 2,378	Interesting Bart, I wonder if gs perform any similar tests before installing... It would be preferable to have the heavy side at the top (imo) when mounted. This would likely cause vertical stringing as oppose to horizontal.

December 4, 2012, 05:35 PM	#29
Erno86 Senior Member Join Date: September 22, 2012 Location: Marriottsville, Maryland Posts: 1,739	A gun barrel...that is placed in the hot sun ---will heat up the barrel on one side --- which will cause a different point of impact, to a gun that was not placed in the sun.