I finally had an over pressurization event.

[cp1969]

Setback was discussed in G&A or Shooting Times a long time ago. I think they mainly focused on the .380 and 9mm and got some astronomical pressure increases.

One more reason why I like revolvers. They suffer "setback" in the opposite direction; ie the bullet comes out of the case. Might tie up the gun but at least it won't cause a big pressure spike.

 

[Hoptob]

You could be right, guys. I just find it hard to believe the numbers. To put this into prospective, here is a picture of Remington 0.357" 140 gr. SJHP.

Width of the cannelure band on this bullet is 0.05". If predictions were correct, sitting bullets at the top and at the bottom of the band would result in 30% difference of max pressure. It's possible but sure hard to believe...

Without knowing more I think Dennis had correct explanation in his original post - partial activation of the powder release. I had a similar accident on 550B and ended up double charging 9 mm case. Here is what happened:

I traded my press for 650 to have a powder check die. It caught a few squibbs but no double charges yet

Mike

 

[dennis40x]

All things being possible setback may have occurred and can’t be ruled out. The taper crimp die is so adjusted that the occurrence is less likely to be contributing factor.

Years ago I made a device to check just that. The device was composed of a tubular housing, bullet seating stem, spring (with a known rate of deflection), and calibrated plunger. Simple to operate insert the case with no primer or propellant but a seated bullet crimped in place. Press the plunger down till the calibration mark dependent on bullet style was flush with the housing. Check the dummy case and bullet for OAL length. If no change occurred then the crimping die was properly adjusted.

The powder charge is the nettlesome aspect to me. This I believe was the primary cause. At some point the set powder charge was exceeded enough to cause the bulged case and pierced prime. The percentage amount of the over charge is not known. (My theory and I could be wrong)

All that is known is that the over pressurization event did not result in catastrophic failure of the case. How close the event came to catastrophic failure I don’t know and replication of the event is not on my things to do list.

Yesterday at the range @ 25yards standing 5.7Gr – W231 load employed in an S&W 4506. Eight magazines of (8) for a total of (64)