Many of the traditional rifles are coned at the base of the breech. They sell a "bore scraper" that will reach down in there and you turn it in a clockwise motion and it basically scrapes any powder residue out of the cone. Or a simple 30-35 caliber cleaning brush on the end of the ramrod will also reach down in there and scrape the cone area clean.

Normal barrel flushing does clean 99% of the buildup most the time. As after I clean, I have used my bore scraper and got nothing out of the barrel.Other times if you scrape the bore turn the barrel over and tap it on a piece of white paper towel you will see stuff fall out of the barrel. Another method is to take a .22 caliber brush, wrap a patch around it, dip that in solvent, and again push to the bottom and twist in a clockwise direction. This will also clean the cone of the bore.

I know Lyman and Thompson Center I was told have a cone. Whether Traditions and CVA also, I will not swear to. I still clean them like they do have one for MY peace of mind. I scrape the cone about every fourth or fifth cleaning. There is not a large build up but better safe then sorry.