Letter Re: Ruptured Case Extractors?

I always see broken shell extractors for sale on web sites and at gun shows. I have yet to ever see a need for one. Do you have any experience in the need for one?
Also, exactly how do they work? Would one for a .30-06 work for a .308, or a 7.62×39, or vice-versa?
I have pondered this for a while, and am hoping you or a fellow reader might be able to answer this.
Also, what causes the need for one? Would a dirty chamber cause a cartridge case to stick in the chamber, thereby ripping the bolt extractor off the bolt, or just tearing the base off the case?
Talk of spare parts is good, but how to avoid needing them might save one’s needing a part at a critical moment.
– Sid, near Niagara Falls

JWR Replies: Your surmise was correct. Broken shell extractors are are indeed used in instances when a case head (the rear half of a cartridge case) completely separates. Head separations are common when bass has been reloaded too many times, or with rifles that suffer from excess headspace. Unlike simple a extractor “rim tear through” where a cleaning rod can be used to remove a stuck piece of brass, when a head completely separates, there is nothing for a cleaning rod to “catch.” In the event of a head separation, the tool is inserted into the chamber from the breech, and tightened with a screwdriver–or perhaps the rim of a cartridge case. It expands and grabs the front half of the case. A cleaning rod can then be inserted (at the muzzle) and the brass ejected.

A .30-06 broken shell extractors can be used in a .308, but not vice versa.  I recommend getting a proper-fitting broken shell extractor for each high powered rifle in your firearms battery.