Re: has anyone had this problem
As young timer indicatess, you have run up against one of the Fundamental metaphysical rules of muzzleloading.
Yes some old timers resorted to "venting" their percussion guns. It is to drill a very small hole into the drum below the nipple. (I have an old original perc gun that was "vented". I have never found such a drastic step necessary. First of all, are you using loose powder? When you pour in the powder, do you give the gun a few raps on the side with your palm so that the powder settles into the drum? I don't buy the "vapor lock theory" There is some problem with the flame of the cap getting to the powder. flash channels to small, restricted by dirt or grease, powder not getting into the drum beneath the nipple etc. Now, all that being asked, have you ever replaced the screw that goes into the end of the drum? If you put in a screw that is too long, it can block (either totally or partially) the flame coming from the nipple into the drum. Do you fire two or three caps before loading to burn oil and grease from the flash channel to be sure the gun is ready for loading. Are you using Pyrodex, which takes a higher temp to ignite? Or pellets, With pellets, the flash has to go down through the nipple, make a 90 degree turn in the drum and then travel into the barrel. In some of the older CVA gunns, made in the same factory as some tradition guns. The drum actually went all the way through to the other side of the barrel and only had a small opening for the flash to go from the drum to ignite the powder charge, and the flash had to make a second 90 degree turn to ignite pellets. In those cases the drum actually goes back to a slightly larger hole drilled in from the face of the breech plug.