Dpms LR-308 Headspace changes after chambering - Page 3

Bart B. · July 26, 2014, 08:22 AM

Put a rod in the bore that's a little shorter than barrel length. With the rifle muzzle up, measure the depth from muzzle to rod tip with the bolt closed and it's locking lugs seated.

Push the bolt forward as far as it'll go then measure low much it's end is closer to the muzzle.

Or, just close the bolt on an empty chamber then push it back and forth without raising the bolt. Estimate or measure how much the bolt moves front to back.

The bolt is all the way back when chamber headspace is measured. If a case with headspace equal to, or a couple thousandths less, chamber headspace is in the rifle, anything that pushes on the case head before the bolt is closed can drive that case deeper into the chamber setting its shoulder back and lengthening its neck. If the bolt closes on the case without setting its shoulder back, the firing pin will do that as it impacts the primer.

Go measure all that stuff with primed cases then witness reality.

Metal god · July 26, 2014, 10:18 AM

To be fair and clarify . The total .0115 set back never happened with one case . It's the difference of all cases tested . The most set back one case had after multiple chambering is .007 .

243winxb · July 27, 2014, 07:04 AM

Looks like the shoulder is going to be pushed back on chambering, no matter what you do. Doesnt matter what the starting head to datum length is? Very strange. Wish i stll had my M16 to test it. Checking 3 bolt actions, 2Rem, 1Savage, the bolts dont move. The head on the Savage bold does move.

Bart B. · July 28, 2014, 08:43 AM

243, it's typically the front edge of the extractor contacting the case rim several hundredths of an inch before the bolt face does that pushes the chambered case hard against the chamber shoulder before the bolt goes into battery. Measure the distance from a bolt face to the same diameter point relative to the firing pin hole as a case rim is. It's often near 1/10th of an inch. Until that extractor snaps over the case rim, the case is hard against the chamber shoulder. Depending on how fast the bolt goes forward starting at that point, the amount of shoulder set back will be directly related to it. And the amount of force needed to push the extractor claw back until it snaps over the case rim makes a difference, too. Slowly closing a bolt won't set the case shoulder back, Fast and furious is a different story.

243winxb · July 28, 2014, 06:56 PM

Quote:

Metal god- It still does it with both the ejector and the extractor removed .

Yes Bart B. i suspect the bump from the extractory would do it also. If the head to datum is longer than the chamber, its going to get bumped back for sure .

F. Guffey · July 28, 2014, 07:26 PM

Seek wisdom, find those things you can not do, find the things you can not change then seek the wisdom to understand the things you have no control over.

This stuff does not lock me up nor does it drive me to the curb.

We need a rifle with an adjustable bolt face, chamber a round, then adjust the slack out of it. We could think of adding a pulse damper.

I have bolts with adjustable bolt faces, they are not for everyone.

F. Guffey

Bart B. · July 28, 2014, 07:57 PM

Cartridges whose rim slides up behind Mauser type external extractor claws as they're loaded from box magazines rarely have any shoulder setback when chambered. Only when they're pushed into the chamber ahead of the extractor does chambering cause case shoulder setback.

F. Guffey · July 28, 2014, 08:13 PM

Quote:

Cartridges whose rim slides up behind Mauser type external extractor claws as they're loaded from box magazines rarely have any shoulder setback when chambered. Cartridges whose rim slides up behind Mauser type external extractor claws as they're loaded from box magazines rarely have any shoulder setback when chambered. Only when they're pushed into the chamber ahead of the extractor does chambering cause case shoulder setback. does chambering cause case shoulder setback.

Quote:

Only when they're pushed into the chamber ahead of the extractor does chambering cause case shoulder setback.

Now you are claiming the Mauser is a push feed and a control feed?

F. Guffey

Bart B. · July 28, 2014, 08:42 PM

No.

cerralvo78 · July 30, 2014, 02:08 PM

WOW...i did not know how long this thread got

lots of good information, thanks to all of you.............what about neck tension on a semi-auto should i crimp or not crimp??

Bart B. · July 30, 2014, 02:25 PM

You don't need to crimp 30 caliber case mouths onto bullets for semiautos. The arsenals loading .30-06 match ammo decades ago learned that. Commercial match ammo for semiautos was seldom crimped and that so made didn't shoot very accurate.

With enough neck grip on the bullet, all's well.

July 26, 2014, 08:22 AM	#51
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Put a rod in the bore that's a little shorter than barrel length. With the rifle muzzle up, measure the depth from muzzle to rod tip with the bolt closed and it's locking lugs seated. Push the bolt forward as far as it'll go then measure low much it's end is closer to the muzzle. Or, just close the bolt on an empty chamber then push it back and forth without raising the bolt. Estimate or measure how much the bolt moves front to back. The bolt is all the way back when chamber headspace is measured. If a case with headspace equal to, or a couple thousandths less, chamber headspace is in the rifle, anything that pushes on the case head before the bolt is closed can drive that case deeper into the chamber setting its shoulder back and lengthening its neck. If the bolt closes on the case without setting its shoulder back, the firing pin will do that as it impacts the primer. Go measure all that stuff with primed cases then witness reality. Last edited by Bart B.; July 26, 2014 at 08:27 AM.

July 26, 2014, 10:18 AM	#52
Metal god Senior Member Join Date: April 10, 2012 Location: San Diego CA Posts: 6,876	To be fair and clarify . The total .0115 set back never happened with one case . It's the difference of all cases tested . The most set back one case had after multiple chambering is .007 . __________________ If Jesus had a gun , he'd probably still be alive ! I almost always write my posts regardless of content in a jovial manor and intent . If that's not how you took it , please try again .

July 27, 2014, 07:04 AM	#53
243winxb Senior Member Join Date: July 26, 2011 Location: USA Posts: 1,730	Looks like the shoulder is going to be pushed back on chambering, no matter what you do. Doesnt matter what the starting head to datum length is? Very strange. Wish i stll had my M16 to test it. Checking 3 bolt actions, 2Rem, 1Savage, the bolts dont move. The head on the Savage bold does move.

July 28, 2014, 08:43 AM	#54
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	243, it's typically the front edge of the extractor contacting the case rim several hundredths of an inch before the bolt face does that pushes the chambered case hard against the chamber shoulder before the bolt goes into battery. Measure the distance from a bolt face to the same diameter point relative to the firing pin hole as a case rim is. It's often near 1/10th of an inch. Until that extractor snaps over the case rim, the case is hard against the chamber shoulder. Depending on how fast the bolt goes forward starting at that point, the amount of shoulder set back will be directly related to it. And the amount of force needed to push the extractor claw back until it snaps over the case rim makes a difference, too. Slowly closing a bolt won't set the case shoulder back, Fast and furious is a different story.

July 28, 2014, 07:26 PM	#56
F. Guffey Senior Member Join Date: July 18, 2008 Posts: 7,249	Seek wisdom, find those things you can not do, find the things you can not change then seek the wisdom to understand the things you have no control over. This stuff does not lock me up nor does it drive me to the curb. We need a rifle with an adjustable bolt face, chamber a round, then adjust the slack out of it. We could think of adding a pulse damper. I have bolts with adjustable bolt faces, they are not for everyone. F. Guffey

July 28, 2014, 07:57 PM	#57
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Cartridges whose rim slides up behind Mauser type external extractor claws as they're loaded from box magazines rarely have any shoulder setback when chambered. Only when they're pushed into the chamber ahead of the extractor does chambering cause case shoulder setback.

July 28, 2014, 08:42 PM	#59
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	No.

July 30, 2014, 02:08 PM	#60
cerralvo78 Junior Member Join Date: July 24, 2014 Posts: 12	WOW...i did not know how long this thread got lots of good information, thanks to all of you.............what about neck tension on a semi-auto should i crimp or not crimp??

July 30, 2014, 02:25 PM	#61
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	You don't need to crimp 30 caliber case mouths onto bullets for semiautos. The arsenals loading .30-06 match ammo decades ago learned that. Commercial match ammo for semiautos was seldom crimped and that so made didn't shoot very accurate. With enough neck grip on the bullet, all's well.