Take a small roll of electricians tape in your pack. Put one strip over the end of the muzzle coming from one side of the barrel about an inch from the muzzle up over the top of the barrel and down the other side. Leave about an inch on the other side and pull the tape until it breaks off and rub it smooth to the surface of the barrel.
I've tested it on targets and if there is any effects it is extremely minimal and is completely safe to shoot through. If it's stayed no through the day and looks to be fine at night, no reason to remove it to just put another piece on in the morning. If it is really wet (rain & snow), still a good idea to take it off at night to let circulation dry out any moisture possibly present inside the barrel. Some small amount could get in from the chamber side. Put a new piece of tape on in the morning. It does work!