When you say the trigger box is loose, do you mean the screws holding it to the reciever are loose? If that's the problem, that would cause slam firing, ecpecially with a heavy spring like that. Are you using the 45 degree sear system or the 90 degree? If they are 45 degree sears you can't use any spring that gives you over about 450 fps because it just can't handle it. May I ask what parts you have in the cylinder and what trigger it is (stock, z-trig, etc.)?