RE: halfcock not working..............
Yes the 1" barrel from Green Mountain or a T/C Hawkins will fit the stock of the .54 caliber Renegade.
Some things to do to fix/check the half cock. First off pull the lock off the rifle and make sure it is well cleaned back there. I like to scrub it with an old tooth brush and some solvent. Then a very light coating of gun oil, on a Q-tip wipe the back of the lock off good. This is when you inspect the back of the lock, if there is some part of the lock broken then you need to send it back to Thompson Center for Warranty.
Pull the rifle (on an empty rifle of course) to full cock. Now holding the hammer, press the trigger and lower the hammer part way. Release the trigger and pull back on the hammer. Some times that will trip the half cock. BUT.. if you start to cock the hammer and do not hear or feel that definate first click where the half cock lies, I think I would send it back to Thompson Center and have them check the rifle over.