It is not that hard to re-solder the muzzle gap, I use an electric soldering gun and flux cored Force 44 solder from Brownells. Finish by carefully filing.
If you absolutely don't want to solder, try the old stand-by, JB Weld. Degrease the area and use a wad or paper towel or cloth patch to make a dam about 1/4" below the muzzle then fill up with the epoxy. May eventually fall out but easily replaced.