Headspace and case stretch

[bigedp51]

You do not need to load a live primer and fire it in your rifle. You use a fired spent primer as I stated in my posting and let the bolt face seat the primer. And the amount the primer is protruding will be your head clearance or the air space between the rear of the case and the bolt face. And this will be how far the case can stretch when fired.

Below is checking head clearance and headspace on a 30-30 Winchester. And if you add the rim thickness to the primer protrusion you will have the rifles actual headspace.

So again the shoulder location on a new unfired rimmed or belted case means nothing. And what does matter is the amount of head clearance you have and if special fire forming methods are needed.

Below on the far left is a new unfired .303 British and its shoulder is approximately a 1/4 inch shorter than the fired case in the center. The case on the far right was full length resized with maximum shoulder setback and failed after the 3rd firing. Meaning the case was fired three times with .009 head clearance and stretched beyond its elastic limits. This is why you only bump the shoulder back .001 or .002 and keep the case from stretching in the base web area.

 

[Lefty G-gear]

You can't judge case shoulder location on new rimmed and belted cases.

Below is a new unfired .303 British case in a Wilson case gauge. And the case would drop further into the gauge but the rim is stopping it from moving further. The Enfield rifle this case will be fired in will not close on a NO-GO gauge but still has .009 head gap clearance due to the case rim thickness.

Below the case belt manufacturing headspace can vary .008 and the chamber headspace can vary .007. And the NO-GO gauge is .224 so you can see the case belt will make the biggest difference in head clearance.

You can take a new unfired case and measure from the case mouth to the base of the case. And then take a fired spent primer and start the primer into the primer pocket with just your fingers.

Now chamber the case and let the bolt face seat the primer and extract the case. Then measure the case from the case mouth to the base of the primer and subtract the first case measurement from the second. And this will be your head clearance or air space between the rear of the case and the bolt face. And this will be how far the case will have to stretch on the first firing to contact the bolt face. Meaning the case shoulder location means nothing until the case is fired. And what is important is your head clearance with new cases and not the shoulder location.

OK.
But I'd like to try one of these for 7mm RM.
HORNADY CASE GAUGE FOR .300 WM $17.48
https://www.midsouthshooterssupply....300-winchester-mag-(point308)-cartridge-gauge

 

[bigedp51]

OK.
But I'd like to try one of these for 7mm RM.
HORNADY CASE GAUGE FOR .300 WM $17.48
https://www.midsouthshooterssupply....300-winchester-mag-(point308)-cartridge-gauge

You use the Hornady cartridge case headspace gauge to measure fired cases. Then you adjust the die for minimum shoulder bump for long case life.

Rimmed and belted cases are older designs when manufacturing tolerances were sloppy by today's standards. And the shoulder shape and location was not important. Below are .450 Henry-Martini cartridges, the case on the left is a modern cartridge and the case on the right is from the 1879 Zulu war.

Below it is the rim or belt that stops forward movement of the cases until the case has been fired and the shoulder is blown forward. And at the bottom is a modern bottle neck case headspaces on its shoulder. "BUT" with all three type cases it is your head clearance on the fired cases that effects case life.

Below a .303 British commercial cartridge being fired in the larger military chamber. And showing the shoulder being blown forward and the case stretching in the rear.



Below is a neck sized .303 British case with its shoulder holding the case against the bolt face. And why you want minimum shoulder bump on full length resized cases and well within the case brass elastic limits.

And again, no matter what type case and how it headspaces in the chamber it is the amount of head clearance that will allow the case to stretch and fail. And as a example I have had new .243 cases that were .009 shorter than my GO gauge. And I simply seated the bullets long and jammed into the rifling to hold the case against the bolt face.

 

[Lefty G-gear]

You use the Hornady cartridge case headspace gauge to measure fired cases. Then you adjust the die for minimum shoulder bump for long case life.

Rimmed and belted cases are older designs when manufacturing tolerances were sloppy by today's standards. And the shoulder shape and location was not important. Below are .450 Henry-Martini cartridges, the case on the left is a modern cartridge and the case on the right is from the 1879 Zulu war.

Below it is the rim or belt that stops forward movement of the cases until the case has been fired and the shoulder is blown forward. And at the bottom is a modern bottle neck case headspaces on its shoulder. "BUT" with all three type cases it is your head clearance on the fired cases that effects case life.

Below a .303 British commercial cartridge being fired in the larger military chamber. And showing the shoulder being blown forward and the case stretching in the rear.



Below is a neck sized .303 British case with its shoulder holding the case against the bolt face. And why you want minimum shoulder bump on full length resized cases and well within the case brass elastic limits.

And again, no matter what type case and how it headspaces in the chamber it is the amount of head clearance that will allow the case to stretch and fail. And as a example I have had new .243 cases that were .009 shorter than my GO gauge. And I simply seated the bullets long and jammed into the rifling to hold the case against the bolt face.

Quote: "You use the Hornady cartridge case headspace gauge to measure fired cases. Then you adjust the die for minimum shoulder bump for long case life."

Right. - we're talking about a FL (Full Length) Sizer Die - right?
And the bolt closes easier than on fire-formed Neck Sized cases? - Yes? (For hunting and sniper applications - vs - bench?)