Re: A ? about brakes
The items suggested by the others in previous obviously work and work well. Just to add the the discussion though, I have used tape on several occasions with no (known anyway) side effects.
When I am on a horseback hunt where the rifle must be in a scabbard I like to use tape. The other methods mentioned tend to pull off the barrel when pulling the rifle from the scabbard. Scabbards are bad about catching all kinds of sticks, leaves and other assorted "stuff" that all goes to the end. I now bring my own scabbard on any horseback hunt to minimize this and to be sure I have a scabbard my rifle will fit in. I digress from the original question.........
In such cases I use electrical tape. One short piece is stretched tight over the bore, then a tight continuous wrap is applied starting at the bore down past the brake. When it is time to shoot, if time allows I remove the tape. If it does not, I shoot with it on.