Anyone have a clue why this is occurring?

[230RN]

That's an interesting one, Elkins45. Unless it's due to burrs from the saw cuts, the bottom side looks like it's slightly thicker than where the blowout occured. I note that the pressure seemed to be a bit low, according to the primer. Makes sense if the pressure were relieved through the hole.

Keep in mind that not every single case in a box is necessarily drawn from the same paired punch and die. The dies and punches are ganged in production so that each stroke of the press forms maybe 5-6 cases at once (or more). So there may have been one or two in that box which was drawn out with a slighly off-center punch and all the circumstances converged to cause that one failure out of the box, all according to Murphy's Law.

Would like to hear details about the rifle used.

Garand took great pains to design the M1 so that there was a minimum of unsupported case overhang from the chambers --in other words, the little thin brass bottle I mentioned was almost completely surrounded by steel.

As a consequence, in experiments to try to wreck the M1, they went up to proof loads of 125,000 (CUP) psi*, which were the highest they could achieve in the .30-06 case, without case failure. They had cracked bolt lugs and other things, but the cases held and the rifle did not blow up.

Terry, 230RN

* Without looking it up, I believe the normal proof load was around 70,000 CUP psi.

 

[Elkins45]

The details are here: http://www.thehighroad.org/showthread.php?t=619628

Cliff's Notes version is that it was a left handed Savage 110.

 

[Baryngyl]

If I still have them after moving twice, I have 3 30-06 cases that are like that, they were very old factory made 220 grain round nose loads, they were pretty well darkened cases but not any corrosion or green on them, I had just wiped them good to make sure there was not dirt/grit on them.

When fired they ended up looking like that, IIRC 1 of them had 2 holes in and 2 had 1 hole each, only one of them let any gas escape from the chamber and hit me in the cheek a bit.

The only thing I could come up with was they were just really old and must have somehow pitted from the inside weakening them.


Michael Grace

 

[ontarget]

I may be wrong but I thought I read in my Lyman manual that undercharging a case can also cause overpressure. Much like failure to fully seat a muzzleloader projectile will cause big problems. The OP said he was below starting load sooooo maybe a possibility.

 

[double bogey]

I encountered cuts like that on the shoulder of some 15 year old hornady custom 139gr
7mm rem mag loads. Hard extraction and bolt opening, I tossed the remaining 12 or so in the recycle bucket. 15 years ago these loads shot very accurate, and fast.

I never could duplicate the speed of these factory rounds without pressure problems (15 years ago), although I could reload just as accurate.