The original flash hole was not on the end. It is below the end about 0.20". It worked real real good with BH, but wasn't perfect. It is conceivable to me, that you may have made your plug less compatible with BH than it was when it was new, by putting the flash hole out on the end. It doesn't really matter, because you use 777, not BH209.

Myself, i use BH209 exclusively, and all my rifles must be 100% reliable with the BH209 powder. This is why the flash hole in the breech plug for my Triumph is 0.46" from the end of the plug. This requires one to turn the diameter of the ventliner smaller, which is no big deal.