Re: Remington Model 7400 trouble's
It sounds like the hammer is following down, so the rifle won't fire the second shot. That is a pretty common result of someone trying to do a "trigger job" and messing up. The hammer will follow down in firing, but will hold with the slower manual operation of first loading the gun.
Try this. FIRST, MAKE SURE THE GUN IS UNLOADED! Then cock it as if loading it. Then bounce the gun butt on a solid surface, like the floor and see if the hammer falls. If it does, see above. You will likely need a new sear and/or hammer. Replacing the parts is not hard, but if you are not comfortable with DIY, take the gun to a gunsmith.