Overload, The first few times I cycled the bolt on my SMLE, I had to get used to that tension of cocking the firing pin while still trying to lock and load the next round. I stripped the bolt off and de-greased, cleaned and lubed the bolt and rails it slides on. Worked it a whole bunch and it eventually smoothed out. If you want to cycle the bolt to work in lube or whatever, without having to cock the firing pin, hold the down the trigger, and the cocking mechanism will not engage, so you are free to operate the bolt without cocking the rifle.