Rockdoc's safety test using a double charge is very sensible since that possibility does exist if you are not careful when loading. Loading two barrels compounds the possibility of a double charge screw-up.
One way to avoid this is to scribe a line on your ramrod even with the muzzles once you have established a load. Then make a habit of quickly checking that you are very close to that line every time you ram a load. Anything short or long of your mark means it's time to pull that load with your worm.
Don't do as a friend of mine did, and leave your ramrod in the bore. Nice guy that I am, I stopped him before he sent it downrange. Now there's a little added ejecta to increase breech pressure.
