#1 - Not only what SD says, but the hammer extension (like a weak spring) also slightly slows down what is already a very slow lock time in the TC's. Gives the shooter more time to wander off target before the boom.
#2 - Can't agree Catfish. While you did catch that this round is intended to headspace off the rim and not the shoulder (including while fireforming), headspacing can still be a cause of misfires if there is wear in the barrel pivot, worn or poorly fitted locking bolts, wear on the frames breech face where they lock up, etc that all affect headspacing. If the case moves when struck by the firing pin because it is not headspaced correctly, a misfire is very possible.
#3 - A worn (not just broken) firing pin on primers that are known to have harder cups is a common cause of misfires with TC's. Another can be gunk buildup that prevents the smooth movement of the firing pin(s) within the frame, and as suggested a weak hammer spring that could have been accelerated by using the hammer extension.
TC frames are all too often neglected by their owners. Kind of like a car, the lawn mower, and that fruit cake Aunt Martha sent you for Christmas in 1972. They take good care of them at first, then just expect it to last forever without that care when the newness wears off. IMO TC frames should be completely stripped, cleaned and re lubed on a regular schedule. It's a perfect opportunity to check parts for wear/breakage and make correction accordingly, besides assuring the frame will last a lifetime or two or three. I dedicate my frames to which barrels are shot on them and so to what they are used for. Easy for me to do because I currently have 20 frames. Back when I shot IHMSA seriously, those frames were done every year. The frames only used for low volume type hunting a couple of times a year or target shooting could go 2-3 years. But the frames for very high volume hunting many times a year got done at least twice a year and sometimes three. A little prevention goes a long ways toward reliability.
Smart might be one way to put it Mike, but I think its more that there are some very experienced TC users on this board who have been at it long enough to have run the gamut on all of the ins and outs of TC's. They're an opinionated bunch who don't always agree with each other, but many of them do know TC's.
