SAAMI head space dimensions- 3006 ? - Page 2

06shooter · March 16, 2015, 10:45 AM

[QUOTE][Back to the bolt closing on a go-gage, what is the length of the chamber from the shoulder to the bolt face?

Have it casted , a no go on the barrel job is what I should have wrote ]

Bart B. · March 16, 2015, 10:47 AM

06Shooter, here's how a 'smith uses .30-06 chamber headspace gauges when rebarrelling;

There's two gauges commonly used; one is the GO (minimum) gauge measures 2.0487" from its head to the shoulder reference, the other's the NO-GO (maximum) gauge that's .010" longer or 2.0587"

The 'smith runs the reamer into the barrel chamber after reaming it to about the correct depth that lets a stripped bolt not close on the NO-GO gauge but will close easily on the GO gauge. If it doesn't close on the GO gauge, he'll ream it a few thousandths deeper, then try again. When that's done, the actual chamber headspace is somewhere between those numbers. Some 'smiths have gauges in .001" increments and when one doesn't let the bolt close on it but another .001" less does, the chamber headspace is somewhere between the two gauge dimensions.

That's the best way to measure actual chamber headspace. Years ago, there were adjustable gauges with a thimble on them graduated in .001" steps. It was set then locked at one dimension then tried in the chamber with a stripped bolt. If the bolt didn't close on it, it was reset to .001" less, then tried again. I used one decades ago I'd borrowed from a 'smith and it was both easy and amazing. My 7.62 NATO Garand's chamber read about 1.6312" as best I could interpolate its thimble adjusted to sub .001" increments.

Most 'smiths like to make chambers close to the GO gauge dimension for best accuracy with new cases and long case life for reloaders.

There's also a .30-06 FIELD (sometimes called FIELD REJECT) gauge that about 2.064" or thereabouts that when used, and the bolt closes on it, the chamber headspace is longer than what's considered safe. Some 'smiths think any chamber headspace dimensioin longer than the NO-GO gauge should not be used.

06shooter · March 16, 2015, 10:54 AM

Do you think manufacturers that claim sub moa accuracy from their hunting rifles are close to min. ?

Bart B. · March 16, 2015, 11:57 AM

No, I don't. Sub MOA accuracy isn't hard to get with most (at least 50% of them) factory rifles shooting their own ammo for a few shots tested properly. Even with chamber headspace near maximum.

They could be anywhere in SAAMI spec range, most likely in the lower range. It needs to be measured if you want good numbers, otherwise compare a fired case + .001" to a GO headspace gauge.

It's unfortunate that everyone testing a given rifle with a given lot of factory ammo will not get the same results.

March 16, 2015, 10:47 AM	#27
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	06Shooter, here's how a 'smith uses .30-06 chamber headspace gauges when rebarrelling; There's two gauges commonly used; one is the GO (minimum) gauge measures 2.0487" from its head to the shoulder reference, the other's the NO-GO (maximum) gauge that's .010" longer or 2.0587" The 'smith runs the reamer into the barrel chamber after reaming it to about the correct depth that lets a stripped bolt not close on the NO-GO gauge but will close easily on the GO gauge. If it doesn't close on the GO gauge, he'll ream it a few thousandths deeper, then try again. When that's done, the actual chamber headspace is somewhere between those numbers. Some 'smiths have gauges in .001" increments and when one doesn't let the bolt close on it but another .001" less does, the chamber headspace is somewhere between the two gauge dimensions. That's the best way to measure actual chamber headspace. Years ago, there were adjustable gauges with a thimble on them graduated in .001" steps. It was set then locked at one dimension then tried in the chamber with a stripped bolt. If the bolt didn't close on it, it was reset to .001" less, then tried again. I used one decades ago I'd borrowed from a 'smith and it was both easy and amazing. My 7.62 NATO Garand's chamber read about 1.6312" as best I could interpolate its thimble adjusted to sub .001" increments. Most 'smiths like to make chambers close to the GO gauge dimension for best accuracy with new cases and long case life for reloaders. There's also a .30-06 FIELD (sometimes called FIELD REJECT) gauge that about 2.064" or thereabouts that when used, and the bolt closes on it, the chamber headspace is longer than what's considered safe. Some 'smiths think any chamber headspace dimensioin longer than the NO-GO gauge should not be used. Last edited by Bart B.; March 16, 2015 at 11:11 AM.

March 16, 2015, 10:54 AM	#28
06shooter Senior Member Join Date: January 18, 2015 Posts: 165	Do you think manufacturers that claim sub moa accuracy from their hunting rifles are close to min. ? Last edited by 06shooter; March 16, 2015 at 11:31 AM.

March 16, 2015, 11:57 AM	#29
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	No, I don't. Sub MOA accuracy isn't hard to get with most (at least 50% of them) factory rifles shooting their own ammo for a few shots tested properly. Even with chamber headspace near maximum. They could be anywhere in SAAMI spec range, most likely in the lower range. It needs to be measured if you want good numbers, otherwise compare a fired case + .001" to a GO headspace gauge. It's unfortunate that everyone testing a given rifle with a given lot of factory ammo will not get the same results. Last edited by Bart B.; March 16, 2015 at 12:39 PM.

March 16, 2015, 10:45 AM	#26
06shooter Senior Member Join Date: January 18, 2015 Posts: 165	[QUOTE][Back to the bolt closing on a go-gage, what is the length of the chamber from the shoulder to the bolt face? Have it casted , a no go on the barrel job is what I should have wrote ]