If anyone has read "A Rifleman Went to War" * by Captain Herbert McBride, Capt McBride was a pre WW1 Canadian shooter. He relates that he shot his Ross many times in rifle practice, everyone in the units had also, they all had great confidence in the rifle, and it was not till they got into Ypres (St Eloi) that the weapons started jamming. It was quite a surprise to him and to those whose bolts could not be opened. I don't know what sort of testing they did, but the Canadians sure missed something. The Ross rifle was still used as a sniper rifle after it was withdrawn from regular service.
Most comments in this thread are about well known military rifles, and less are about civilian rifles that were built in limited quantity, and fizzled because they were turkeys.
Stuart Otteson’s book “The Bolt Action” Vol II has a number of limited edition turkeys that no one knows about. Read the sections on the Omega II, the Shultz & Larsen Model 68DL, for rifles that were not ready for prime time.
Two models that I would like to know about, were the ones involved in two incidents related to me. The first account was from a Bud who was at the range when a prone shooter had the bolt blow out of his rifle, go through his chin, and through his shoulder Bud said the bolt was picked up 50 yards behind the firing line. Bud said the locking seats were on a pressed in collar in the receiver ring. The collar was not mechanically fastened, it rotated, so when the round was fired, the bolt lugs were not resting on anything. I asked Bud what make, and he just said “some foreign model”.
The second was of a shooter who was testing bullets at either Sierra or Speer. His incident was similar, the rifle was a German rifle (the name was so obscure I could not find it on the web, and since have forgotten it) with a pressed in locking lug insert. During testing the insert rotated, the bolt blew out, going through his forearm. The rifle was in a fixture, and he had his arm over the stock to press the trigger. I was told this while at a rifle match, the unfortunate was shooting on the big end of the range, and I was on the small, I had limited time to do things, so I did not go visit and press the gentleman for details on his accident.
These incidents have made me leery of actions with pressed in locking lug recesses.
* Jamming of the Ross may have been in his first book: The Emma Gees.
Good enough for Government Work.