243 pressure issues

[243winxb]

Fire Forming

Fire Forming. The case will headspace on the false shoulder, which will hold the case against the bolt face when fireforming. This will prevent the case from stretching/thinning and prevent case head separations. The actual false shoulder location will depend on your chamber headspace and the location of the shoulder of the case.
The case mouth is opened with a tapered expander to the next larger caliber. Then run up part way, not fully, into a full length sizing die. The bolt should close with a little resistence. This fire forming is needed when the case headspace, distance from head to datum line on shoulder, is under .010" or more when compared to the chamber of the rifle. This will not help factory ammo brass that has been damaged on the first firing.

 

[Clark]

CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The High Road, nor the staff of THR assume any liability for any damage or injury resulting from use of this information.

Bad day at the range shooting a 243 10 years ago, but I got 30,000 downloads on the picture.

The .243 is SAAMI registered at 60,000 psi max and 78,000 -84,000 psi proof test.

The 243 has the same case head as the 270 registered at 65,000 psi and the 8mmMauser registered at 35,000 psi, but they all have the same case heads with the same strength.

That case head is made out of C26000 brass (cartridge brass)Temper - H06
Tensile yield strength - 65,300 psi.
That brass can be formed into a weak shape, like a 10mm pistol cartridge, or a strong shape like a 38 Special case.
But no matter how beefy around the primer pocket, it is still going to have problems somewhere around it's tensile yield, but that could be over 80,000 psi in the 6mmBR with small primer pocket.

When a rimless brass case fails from pressure, the primer pocket gets loose.
This is the limit that drives the SAAMI registration.
If primer pockets got loose at 100,000 psi, most cartridges would be registered at 90,000 psi.
If primer pockets got loose at 50,000 psi, most cartridges would be registered at 45,000 psi.

The foundation of load data is not built on sand, it is built on tight primer pockets.

The 243 case head can get long brass life in a individual rifle at ~ 67,000 psi with margin for load to load variation, temp variation with powder, dirty chamber, etc.

I have noticed that Varget is not only temperature stable, but it is also very accurately characterized in the Quickload library. No adjustments required.

The extractor groove growth of .001" in one shot will occur at 75,000 psi with Varget in 243.

I can tell you that the difference between 60kpsi and 67 kpsi in 243 is about 1 gr of Varget.

 

[Striker Fired]

What did the bolt face look like after that little "experiment"?

 

[bigedp51]

The last batch of 100 .243 cases I purchased had cases as short as .009 below minimum headspace. Add this to your actual headspace and you can easily have .012 head clearance or "air space" between the bolt face and the rear of the case.

The average full length resizing die is setup to push the shoulder back .002 smaller than minimum headspace, this allows the resized cartridge to fit in any chamber. By using the resizing dies instructions you can be "OVER" resizing these cases and be causing premature case head separations.

I set the full length resizing dies up per the instructions "BUT" I use headspace control shims to "CONTROL" how far the shoulder is actually pushed back (if at all) during resizing.



By placing these shims under the dies lock ring "YOU" control your cartridge case headspace and "WHERE" the shoulder of the case ends up after resizing.





Having some simple gauges and measuring tools can virtually stop any case head separations from happening.

 

[popper]

Rossi in 243? Pick the cases that don't have the shiny line close to the case head, use the paper clip on the inside to see if there is a groove. Use a mild load and shoot them. It will blow the shoulder back out without separation. Make sure the chamber has NO oil in it. Use a once fired factory case to do the partial N/S thing. When the lever closes easily, your done. Smoke and size one of your questionable cases with the SAME die adjustment to see if the shoulder is still too far back. You can check a once fired factory case with a partially seated USED primer to check the H/S, use a pencil or something to fully seat the case in the chamber, close the lever fully. Slowly extract the case and measure how far the primer sticks out. Check against SAAMI specs to see if rifle work needs to be done. You are using a 100 grn SP for piggies, right?

 

[Clark]

Striker Fired
What did the bolt face look like after that little "experiment"?

10 years ago I was bending bolts and truing bolt faces.

But that was before the above pic.

I do not think the gun has been shot since.