A recent article at ITS Tactical, Inc.'s Web site warns of the dangers of using worn-out holsters with certain types of firearms. One caused a pistol to discharge, fortunately without causing serious injury. Here's an excerpt.
The trusty, comfortable, leather holster I had been using for a year and two weeks had done what a baseball glove does after lots of use; It got soft. This particular holster carries the pistol outside the waistband, but inside the belt. The belt slides through slots in the outer side of the holster.
The problem stemmed from the leather on the inner side of the holster getting soft. A crease formed, which eventually was large enough to extend beyond the trigger. Manipulate the gun in just the wrong manner and this crease is no different than a finger on the trigger. Boom!
I can’t say I didn’t know the crease had been formed in the holster. I trained myself to be sure that when holstering, to make sure the gun was fully in the holster, with the trigger protected. On this day, did I forget to do that when I holstered up? Did the leather finally get so soft that a combination of body movements and interference by the cushy leather seat move the Glock enough to create a situation where the trigger was engaged by the holster?
I don’t think we’ll ever know for sure, but I’ll humbly admit to the former as the likely culprit. However, if it was the latter, then those of you who use this type of holster need to be aware of its limitations and the possibility of experiencing what I did.
There's more at the link. The eight photographs accompanying the article are particularly valuable, illustrating the cause of the discharge and its near-tragic effects.
I highly recommend this article (particularly the photographs) to all who carry Glock pistols, and/or others with similar safety devices. A worn holster can cause similar problems with many such weapons. (While you're there, check out some of the other articles on their Web site. They have some good reading.)