By your post, I am assuming that you are shooting a side cocker with a #11 cap. You know what assuming gets you!!
Anyway, on such a M/L , Prior to the initial load, I insert a damp patch all the way down the bore with my Range Rod. I then pop one cap, Pull the rod and check the crud on the patch. That tells me the vent is clear and whether or not, I need to pop another cap. If the patch shows a bunch of mud, I change the patch and pop a second cap. This also allows for a little back pressure to clear the vent back toward the snail head. You also catch all the crud at the patch and keeps it out of the bore. Again, I only do this on #11 or musket caps and have never tried it on a 209 as most if not all of these are inlines.
Be safe!!!