For the first time, using ammo that I have never used before in the 3AT(Sellier Belloit), several cartridges failed to fire--I heard the click of the trigger and the firing pin but "nothing". Looking at cartridge after ejecting, I noticed a slight "dent" in the cartridge, where the pin actually hit the cartridge but it just did not result in a discharge. Asked someone in the gunshop and was told that with the 3AT and its "soft" (I think that was the word) pin, sometimes cartridges can fail to fire. Everything else I tried today (we are now talking about the good stuff--Federal hydra, and speer gold) fired fine. As a matter of fact I reloaded several of the cartridges that did not fire the first time into the mag and they fired this second time. Other S&B cartridges in that box also fired on the first try. Explanations? Comments? Interested in others with similar experience and reasons for same.