Case gauge - Page 2

**Unclenick** · April 14, 2009, 12:01 PM

Gentlemen! Manners, please! Criticism may be satisfying to deliver, but accurate facts are more useful.

A tolerance is a range of dimensions from a minimum acceptable number to a maximum acceptable number. The case has a different tolerance from the chamber. The way most cartridges manage the range is such that the longest case headspace will fit into the shortest chamber headspace, even if a little squeezing is involved. If there is extra room, the brass is allowed to stretch to fill it. Hatcher's Notebook includes an example of a case stretching a sixteenth of an inch in an extra long experimental chamber with no sign of head separation in new military brass.

Anyway, the point is that the longest chamber allowance is greater than the longest cartridge allowance. Thus, a long chamber cannot be relied on to tell you a case is properly sized for the shortest chamber.

Example:
Winchester .308 SAAMI spec
Chamber tolerance limits: 1.630"—1.640"
Case tolerance limits: 1.627"—1.634"

The four thousandths difference between the minimum chamber and the maximum cartridge is apparently figured to be within the capacity of most actions to jam in. Hatch found that rapid bolt operation alone could shorten case sizing something like six thousandths in the .30-06, IIRC?

amamnn · April 14, 2009, 12:09 PM

I loaded for years before I bought a case gage. Then I decided I wanted to shoot accurate ammo.

dmazur · April 14, 2009, 12:25 PM

And, the difference is only 0.004" to 0.006" for GO/NOGO.

Chambering it in an example rifle is a check, and probably is better than no check at all.

However, depending on what your objective is, you may want to resize to SAAMI minimum (guaranteed chambering, shorter brass life), or you may be trying for 0.001" less than once-fired length (longer brass life).

Some recommend loading to SAAMI minimum for gas guns like the Garand, which can slam-fire for a number of reasons. Incorrectly-sized brass is one of them.

**Unclenick** · April 14, 2009, 12:38 PM

It gets more complicated. If you get once-fired brass, the spring-back after coming out of the sizing die of a case extracted from a long chamber can actually fail to meet SAAMI case maximum. I've had that occur. In those instances only a small base die is able to set the shoulder back far enough on a single pass, and quite possibly would be the best choice for commercial work?

freakshow10mm · April 14, 2009, 12:45 PM

That's what I use. Redding made me sizing dies that are similar to the RCBS small base die.

Slamfire · April 14, 2009, 08:26 PM

I have rifle case gages in most of the calibers I reload.

The calibers .223, 308, and 30-06 can be fired in a number of different rifles. For these calibers I size everything to gage minimum.

I have dropped chamber headspace gages into my Wilson cartridge headspace gages. "Go" on the chamber headspace gage corresponds exactly with the "go" mark on the cartridge headspace gage. This is also true for the "no go" gages.

This tells me the Wilson gages are calibrated to a standard, and if the rifle is within headspace, than a case sized according to the Wilson gage should not be undersized, or oversized. Wilson gages only measure length. They are cut wide between the shoulder and the base so you can drop a fired case into the thing and get a good idea of the headspace of your rifle.

I also have reamer cut gages. These gages were cut with the same reamer used by the gunsmith who installed my barrel. These reamers will tell me if my case is too long, or too "fat" after sizing.

The typical advice of turning the die down to touch the shell holder and add an eighth of a turn, is bogus, hit or miss at best. And you will find that out once you have gages to measure what is going on.

April 14, 2009, 12:01 PM	#26
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	Gentlemen! Manners, please! Criticism may be satisfying to deliver, but accurate facts are more useful. A tolerance is a range of dimensions from a minimum acceptable number to a maximum acceptable number. The case has a different tolerance from the chamber. The way most cartridges manage the range is such that the longest case headspace will fit into the shortest chamber headspace, even if a little squeezing is involved. If there is extra room, the brass is allowed to stretch to fill it. Hatcher's Notebook includes an example of a case stretching a sixteenth of an inch in an extra long experimental chamber with no sign of head separation in new military brass. Anyway, the point is that the longest chamber allowance is greater than the longest cartridge allowance. Thus, a long chamber cannot be relied on to tell you a case is properly sized for the shortest chamber. Example: Winchester .308 SAAMI spec Chamber tolerance limits: 1.630"—1.640" Case tolerance limits: 1.627"—1.634" The four thousandths difference between the minimum chamber and the maximum cartridge is apparently figured to be within the capacity of most actions to jam in. Hatch found that rapid bolt operation alone could shorten case sizing something like six thousandths in the .30-06, IIRC? __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; April 14, 2009 at 12:29 PM.

April 14, 2009, 12:09 PM	#27
amamnn Senior Member Join Date: May 13, 2006 Location: WA, the left armpit of the USA Posts: 1,323	I loaded for years before I bought a case gage. Then I decided I wanted to shoot accurate ammo. __________________ "If the enemy is in range, so are you." - Infantry Journal

April 14, 2009, 12:25 PM	#28
dmazur Senior Member Join Date: July 5, 2007 Location: Pacific NW Posts: 1,310	And, the difference is only 0.004" to 0.006" for GO/NOGO. Chambering it in an example rifle is a check, and probably is better than no check at all. However, depending on what your objective is, you may want to resize to SAAMI minimum (guaranteed chambering, shorter brass life), or you may be trying for 0.001" less than once-fired length (longer brass life). Some recommend loading to SAAMI minimum for gas guns like the Garand, which can slam-fire for a number of reasons. Incorrectly-sized brass is one of them. __________________ .30-06 Springfield: 100 yrs + and still going strong

April 14, 2009, 12:38 PM	#29
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	It gets more complicated. If you get once-fired brass, the spring-back after coming out of the sizing die of a case extracted from a long chamber can actually fail to meet SAAMI case maximum. I've had that occur. In those instances only a small base die is able to set the shoulder back far enough on a single pass, and quite possibly would be the best choice for commercial work? __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

April 14, 2009, 12:45 PM	#30
freakshow10mm Junior member Join Date: January 23, 2008 Location: MI Posts: 1,398	That's what I use. Redding made me sizing dies that are similar to the RCBS small base die.

April 14, 2009, 08:26 PM	#31
Slamfire Senior Member Join Date: May 27, 2007 Posts: 5,261	I have rifle case gages in most of the calibers I reload. The calibers .223, 308, and 30-06 can be fired in a number of different rifles. For these calibers I size everything to gage minimum. I have dropped chamber headspace gages into my Wilson cartridge headspace gages. "Go" on the chamber headspace gage corresponds exactly with the "go" mark on the cartridge headspace gage. This is also true for the "no go" gages. This tells me the Wilson gages are calibrated to a standard, and if the rifle is within headspace, than a case sized according to the Wilson gage should not be undersized, or oversized. Wilson gages only measure length. They are cut wide between the shoulder and the base so you can drop a fired case into the thing and get a good idea of the headspace of your rifle. I also have reamer cut gages. These gages were cut with the same reamer used by the gunsmith who installed my barrel. These reamers will tell me if my case is too long, or too "fat" after sizing. The typical advice of turning the die down to touch the shell holder and add an eighth of a turn, is bogus, hit or miss at best. And you will find that out once you have gages to measure what is going on.