before you put your slide on, check and make sure the spring tab isnt already under the disconnect, when you fire without the slide on there might be enough travel in the disconnect to allow the spring to go under and it will to fire with the slide off because there is nothing on top to jam the diconnect . put everything together, including the slide on and then fire it. i've put several triglides in STI's and have had no problem. there is nothing wrong with the back of your sear, if the trigger will set you dont need to take metal off