The problem is not dirt or gunk, it is heat. When a revolver is fired, the cylinder expands from heat, lengthwise as well as in other directions. If the barrel-cylinder gap is too tight, the cylinder binds.
I recommend finding a gunsmith who has the special tool to trim off the end of the barrel and reset the forcing cone, but you can do it yourself if you are very careful. Cover the bottom of the top strap above the forcing cone with masking tape or metallic tape*, put the barrel in a padded vise straight up and down, then use a good, flat file to file the end of the forcing cone. It won't take much, so don't overdo it, and keep the file perfectly level at all times (that is why you want the barrel perfectly vertical).
You want the gap to be even and about .006"-.007".
*A safeside file is best, but not easy to find except from specialty suppliers.
Jim